Add common README sections (#27)

Author: dantleech

README.md

@@ -63,3 +63,16 @@ License
 -------
 
 This project is licensed under the MIT License - see the [LICENSE.md](LICENSE.md) file for details
+
+Contributing
+------------
+
+This package is open source and welcomes contributions! Feel free to open a
+pull request on this repository.
+
+Support
+-------
+
+- Create an issue on the main [Phpactor](https://github.com/phpactor/phpactor) repository.
+- Join the `#phpactor` channel on the Slack [Symfony Devs](https://symfony.com/slack-invite) channel.
+