[no ci] add basic contributing guide

CONTRIBUTING.md

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+# Contributing to CounterStrikeSharp
+
+We'd love for you to contribute to CS# to make it better than it is today!
+
+Here are the guidelines we'd like you to follow:
+
+ - [Question or Problem?](#question)
+ - [Issues and Bugs](#issue)
+ - [Submission Guidelines](#submit)
+ - [Coding Format](#format)
+
+## <a name="question"></a> Got a Question or Problem?
+
+If you have questions about how to contribute to CounterStrikeSharp, please join our [Discord][discord] server.
+
+## <a name="issue"></a> Found an Issue?
+
+If you find a bug in the source code or a mistake in the documentation, you can help us by
+submitting an issue to our [GitHub Repository][github]. Even better you can submit a Pull Request
+with a fix.
+
+**Please see the [Submission Guidelines](#submit) below.**
+
+## <a name="submit"></a> Submission Guidelines
+
+### Submitting an Issue
+Before you submit your issue please search the archive, maybe your question was already answered.
+
+If your issue appears to be a bug and hasn't been reported, open a new issue. Help us to maximize
+the effort we can spend fixing issues and adding new features, by not reporting duplicate issues.
+Providing the following information will increase the chances of your issue being dealt with
+quickly:
+
+* **Overview of the Issue** - if an error is being thrown a stack trace helps
+* **Operating System** - is this a problem with a specific OS (Windows or Linux)?
+* **Reproduce the Error** - provide details, if possible, on how to reproduce the error
+* **Related Issues** - has a similar issue been reported before?
+* **Suggest a Fix** - if you can't fix the bug yourself, perhaps you can point to what might be causing the problem (line of code or commit)
+
+### Submitting a Pull Request
+Before you submit your pull request consider the following guidelines:
+
+* Search [GitHub](https://github.com/roflmuffin/CounterStrikeSharp/pulls) for an open or closed Pull Request
+  that relates to your submission. You don't want to duplicate effort.
+* If adding a feature or enhancement, we recommend you first [start a discussion for
+  it](https://github.com/roflmuffin/CounterStrikeSharp/discussions) before submitting a Pull Request.
+* [Fork](https://help.github.com/articles/fork-a-repo/) this repo.
+* [Clone](https://help.github.com/articles/cloning-a-repository/) your copy.
+    ```shell
+    git clone https://github.com/YOUR_USERNAME/CounterStrikeSharp.git
+    cd CounterStrikeSharp/
+    ```
+* After cloning, set a new remote [upstream](https://help.github.com/articles/configuring-a-remote-for-a-fork/) (this helps to keep your fork up to date)
+
+    ```shell
+    git remote add upstream https://github.com/roflmuffin/CounterStrikeSharp.git
+    ```
+
+* Make your changes in a new git branch:
+
+    ```shell
+    git checkout -b my-fix-branch master
+    ```
+
+* Create your patch and run appropriate tests.
+* Commit your changes using a descriptive commit message that uses the imperative, present tense: "change" not "changed" nor "changes".
+
+    ```shell
+    git commit -a
+    ```
+  Note: the optional commit `-a` command line option will automatically "add" and "rm" edited files.
+
+* Push your branch to GitHub:
+
+    ```shell
+    git push origin my-fix-branch
+    ```
+
+In GitHub, send a pull request to `CounterStrikeSharp:master`.
+If we suggest changes, then:
+
+* Make the required updates.
+* Re-run CounterStrikeSharp to ensure everything is still working & tests are passing.
+* Commit your changes to your branch (e.g. `my-fix-branch`).
+* Push the changes to your GitHub repository (this will update your Pull Request).
+
+If the PR gets too outdated we may ask you to rebase and force push to update the PR:
+
+```shell
+git fetch upstream
+git rebase upstream/master
+git push origin my-fix-branch -f
+```
+
+That's it! Thank you for your contribution!
+
+#### After your pull request is merged
+
+After your pull request is merged, you can safely delete your branch and pull the changes
+from the main (upstream) repository.
+
+[github]: https://github.com/roflmuffin/CounterStrikeSharp
+[discord]: https://discord.gg/eAZU3guKWU