Add common README sections (#6)

Author: dantleech

README.md

@@ -15,3 +15,16 @@ $ ./vendor/bin/var-dump-server localhost:9912
 ```
 
 Use the `dump()` function to dump to the var-dump-server.
+
+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.
+