Add Contributing section to README.md, remove CONTRIBUTING.md file

Author: vors

CONTRIBUTING.md

@@ -40,4 +40,10 @@ is YAML format. To use this format, follow these steps:
 
 [package_control]: https://sublime.wbond.net/installation
 [this_repo]: https://github.com/SublimeText/PowerShell
-[syntax_topic]: http://sublime-text-unofficial-documentation.readthedocs.org/en/latest/extensibility/syntaxdefs.html
+[syntax_topic]: http://sublime-text-unofficial-documentation.readthedocs.org/en/latest/extensibility/syntaxdefs.html
+
+# Contributing
+
+There are two permanent brances: `master` and `dev`.
+Master always points to the latest release tag. 
+All development is done in `dev` branch, please use it for pull request.