Add documentation about contributing (#184)

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

Author: jacobperron

CONTRIBUTING.md

@@ -1,3 +1,31 @@
+# Contributing to ROS 2 Java
+
+This document contains rules and guidelines for contributing to the ROS 2 Java project.
+
+## How to contribute
+
+Here are a few things you can do to contribute to the project:
+
+1. Report a bug by opening an issue on GitHub
+2. Even better, open a **pull request** fixing the bug!
+
+If you open a ticket, be patient while waiting for a response; The ROS 2 Java team is small.
+While you wait, other excellent ways to contribute include:
+
+1. Leave constructive feedback on an open pull request
+2. Try to reproduce an existing bug report and leave a comment
+
+## Pull requests
+
+Each pull request must satisfy the following requirements before it can be merged:
+
+1. Target the latest developement branch (`main`)
+2. Have one approval from a maintainer
+3. Continuous integration (CI) is building and passing tests
+    - This should be automatically triggered upon opening a pull request
+
+## Note about license
+
 Any contribution that you make to this repository will
 be under the Apache 2 License, as dictated by that
 [license](http://www.apache.org/licenses/LICENSE-2.0.html):

README.md

@@ -159,3 +159,8 @@ Although the `ros2_java_android.repos` file contains all the repositories for th
           -DCMAKE_FIND_ROOT_PATH="${PWD}/install"
 
 You can find more information about the Android examples at https://github.com/ros2-java/ros2_android_examples
+
+## Contributing
+
+Contributions are more than welcome!
+If you'd like to contribute to the project, please read [CONTRIBUTING](CONTRIBUTING.md) for contributing guidelines.