Merge pull request #1485 from AlexDenisov/github_contributing_guidelines

CONTRIBUTING.md copied from wiki pages

CONTRIBUTING.md

+## Contribute to GitLab 
+
+If you want to contribute to GitLab, follow this process:
+
+1. Fork the project
+2. Create a feature branch
+3. Code
+4. Create a pull request
+
+We only accept pull requests if: 
+
+* Your code has proper tests and all tests pass
+* Your code can be merged w/o problems 
+* It wont broke existing functionality
+* Its a quality code
+* We like it :)
+
+## [You may need a developer VM](https://github.com/gitlabhq/developer-vm)
+
+## Running tests
+
+To run the specs for GitLab, you need to run seeds for test db.
+
+    cd gitlabhq
+    rake db:seed_fu RAILS_ENV=test
+
+Then you can run the test suite with rake:
+
+    rake gitlab:test
+