Merge pull request space-ros#87 from ivanperez-keera/readme-contrib-r…

…ules

Document contribution rules (space-ros#76).

CONTRIBUTING.md

@@ -0,0 +1,48 @@
+# Contribution rules
+
+The following subsections address how to contribute to the Space ROS project.
+
+All contributors should follow these rules when submitting contributions to
+Space ROS. These rules have been designed to simplify the process of
+establishing compliance with requirements of space software.
+
+## Commits
+
+- All commits must reference the issue they address. *A consequence of this is
+  that no commits can be made unless there is a corresponding issue for them.*
+
+## Issues
+
+- All issues being addressed must be assigned a milestone (ideally, prior to
+  engaging in the work).
+
+## Milestones
+
+- All releases are tagged with their version number, which also corresponds to
+  a milestone.
+
+## Pull Requests
+
+- All changes are incorporated via pull requests (even changes by the core
+  team).
+
+- All PR merges introduce a separate merge commit (i.e., git merge --no-ff),
+  that closes the issue that the PR addresses, as well as any other issues
+  that are fixed as a side effect, or that can no longer be reproduced after the
+  change. The commit uses the syntax `Closes #<Ref>`, `Fix #<Ref>` or a command
+  supported by github to automatically close the issue.
+
+- There'll be a preference for PRs to address only one issue at a time, but
+  we'll be flexible especially for cases in which a fix addresses multiple
+  related issues at the same time (see point above).
+
+- All PRs must be approved by a maintainer. When the author of the PR is one of
+  the maintainers, a different maintainer must approve the PR.
+
+- All PRs must pass the tests for the repository they are being committed to.
+
+- The commit history must be clean. Contributors and maintainers are
+  recommended to rebase and squash as needed *prior to accepting a PR and
+  merging the changes*, so that the commits present how to introduce the change
+  onto the HEAD in an understandable way (rather than describing all the
+  intermediate steps taken until the final solution was discovered).

README.md

@@ -1,3 +1,8 @@
 <img src="/logos/spaceros_white_on_blue.png" alt="Space ROS Logo - White on Blue" width="700"/>
 
 Documentation is at https://space.ros.org
+
+# Contribution rules
+
+See the [contributing guide](Contributing.md) for details on how to contribute
+to the Space ROS project.