contributing: how people can help

It looks like it was missing.

I initially started a page on our wiki [1], but it looks like this
should be on the website.

Link: https://github.com/multipath-tcp/mptcp_net-next/wiki/Contributing [1]
Reviewed-by: Mat Martineau (@mjmartineau) <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

README.md

@@ -17,6 +17,7 @@ website for those who want to contribute.
 - `faq`, for Frequently Asked Questions.
 - `apps`, the list of currently apps supporting MPTCP natively.
 - `details` contains detailed explanations of the kernel implementation.
+- `contributing`, details for those working on the project.
 
 ## Front matter
 At the top of all pages a section between two `---` lines contains information

contributing.md

@@ -0,0 +1,133 @@
+---
+layout: home
+title: Contributing
+nav_order: 9
+nav_titles: true
+titles_max_depth: 2
+---
+
+## Many ways to contributes
+
+There are many ways to contribute to MPTCP in general:
+- Reporting bugs
+- Testing the development version
+- Talking about it on social media, mailing lists, conferences, etc.
+- Sending supportive messages to other contributors
+- Helping new users on different platforms: mailing lists, IRC, external
+  services
+- Asking to enable it by default on services (servers) and devices
+- Adding [native MPTCP support in apps](apps.html) (or asking app developers to
+  add native MPTCP support)
+- Improving this [website](https://github.com/multipath-tcp/mptcp.dev)
+- Improving [`mptcpd`](https://github.com/multipath-tcp/mptcpd), and tools used
+  to configure MPTCP, e.g.
+  [IPRoute2](https://wiki.linuxfoundation.org/networking/iproute2),
+  [NetworkManager](https://networkmanager.dev/), etc.
+- Sponsoring the maintainers (e.g. on [GitHub for Matt](https://github.com/sponsors/matttbe))
+- etc.
+
+And of course, contributing to the Linux kernel itself, see below.
+
+## Kernel development
+
+This part is for kernel developers: modifying MPTCP in the Upstream Linux
+kernel. Patches with new features and bug fixes are of course welcome.
+
+### Testing the modifications
+
+It is easy to build the kernel, the dependences, and start a VM thanks to
+[MPTCP Upstream Virtme Docker](https://github.com/multipath-tcp/mptcp-upstream-virtme-docker).
+With just one command, you can get a prompt from a VM using the modified kernel
+or run the whole test suite. For more details, please see this
+[page](https://github.com/multipath-tcp/mptcp_net-next/wiki/CI) from our wiki.
+
+
+{: .note}
+Any push to a fork of the [`mptcp_net-next`](https://github.com/multipath-tcp/mptcp_net-next)
+repository on GitHub will trigger the CI: look at the `Actions` tab in the fork
+repository to follow the progress, and show the results.
+
+### Patches are shared on the mailing list
+
+#### Why?
+
+Like many kernel subsystems, patches can be sent to the assigned mailing list
+([[email protected]](mailto:[email protected])), and **not** via Pull
+Requests on GitHub. The idea is not to restrict access to people who have a
+GitHub account, and to have a decentralized system.
+
+#### It is easy with `b4`
+
+Sending patches by email is **not difficult**, no more than setting up a
+GitHub account, with the verification of the email address, a new SSH key, etc.
+
+To help with this task, we recommend using
+[b4](https://b4.docs.kernel.org/en/latest/contributor/overview.html). After
+having [installed](https://b4.docs.kernel.org/en/latest/installing.html) it, you
+need to either:
+- configure the
+[web-endpoint](https://b4.docs.kernel.org/en/latest/contributor/send.html)
+(launching 3 commands)
+- or set info about your [SMTP server](https://git-send-email.io/#step-2) in the
+  git config file
+
+#### Workflow
+
+The workflow is then easy: use
+[`b4 prep`](https://b4.docs.kernel.org/en/latest/contributor/prep.html) to
+create a new branch, and
+[`b4 send`](https://b4.docs.kernel.org/en/latest/contributor/send.html) to send
+your patches by email.
+
+In short, once `b4` has been installed and configured, the workflow looks like:
+
+```bash
+git switch export # or export-net for fixes
+b4 prep -n <new branch name>
+# edit your code
+git add -p && git commit -s
+./scripts/checkpatch.pl -g HEAD ## check the output, fix issues with 'git commit --amend'
+b4 prep --edit-cover # if you have more than one patch
+b4 send --reflect # check if the mails you sent to yourself are OK
+b4 send
+```
+
+Once sent, the patches will be tested by our CI. A report will then be posted on
+[Patchwork](https://patchwork.kernel.org/project/mptcp/list/?state=*). See the
+[CI](https://github.com/multipath-tcp/mptcp_net-next/wiki/CI) page on our wiki
+for more details.
+
+### Commit messages
+
+Please **always** include the reason why a patch is needed: we can easily list
+the modifications by looking at the patch itself (`diff`), but understanding why
+a modification has been done, why it has been done this way and not another one,
+etc. is important context for reviewers and future maintenance. This information
+should appear in the commit message.
+
+For more details, please check the [kernel
+doc](https://www.kernel.org/doc/html/latest/process/submitting-patches.html)
+page.
+
+Do not hesitate to look at the Git history to get some examples.
+
+### Code style
+
+It is the same as the guidance for Netdev, see their
+[FAQ](https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html) for
+more details.
+
+#### tl;dr
+
+* Designate your patch for a specific tree - `[PATCH mptcp-net]` or `[PATCH mptcp-next]`,
+  see the [Patch prefixes](https://github.com/multipath-tcp/mptcp_net-next/wiki/Patch-prefixes)
+  page for more details.
+* For fixes, the `Fixes:` tag is required, regardless of the tree.
+* Don't post large series (> 15 patches), break them up.
+* Don't repost your patches within one 24h period.
+* [Reverse Xmas tree](https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs)
+  for the variable declaration (from longest to shortest lines).
+* Use [`checkpatch.pl`](https://www.kernel.org/doc/html/latest/dev-tools/checkpatch.html),
+  e.g. `./scripts/checkpatch.pl -g HEAD`
+* Use [`shellcheck`](https://www.shellcheck.net) for the Shell scripts.
+* Keep the same style as the surrounding code.

details.md

@@ -18,9 +18,9 @@ where the behavior is modified using TCP-ULP.
 MPTCP listen sockets will create "plain" *accepted* TCP sockets if the
 connection request from the client didn't ask for MPTCP.
 
-If you are interested by **contributing to the kernel**, please check this
-[wiki](https://github.com/multipath-tcp/mptcp_net-next/wiki/Contributing) page
-and this [MPTCP Upstream Virtme Docker](https://github.com/multipath-tcp/mptcp-upstream-virtme-docker)
+If you are interested by **contributing to the kernel**, please check the
+[Contributing](contributing.html) page and this
+[MPTCP Upstream Virtme Docker](https://github.com/multipath-tcp/mptcp-upstream-virtme-docker)
 repo.
 
 This page needs to be improved, feel free to

index.md

@@ -187,3 +187,4 @@ for more details.
 * [Continuous Integration](https://github.com/multipath-tcp/mptcp_net-next/wiki/CI)
 * [Testing](https://github.com/multipath-tcp/mptcp_net-next/wiki/Testing)
 * [Issue tracker](https://github.com/multipath-tcp/mptcp_net-next/issues)
+* [Contributing](contributing.html)