Add contribution guide

CONTRIBUTING.md

+# Contributing to gitlab-cloner
+
+## Copyright and Management
+
+The original author, Hermann Krumrey, has the absolute authority on the management
+of this project and may steer the development process as he sees fit.
+
+Contributions will be attributed to the author of said code and the copyright will
+remain the author's.
+
+## Coding guidelines
+
+**Testing**
+
+As this is a simple script, unit tests are not required. Tests are done in the
+way of automated gitlab builds.
+
+**Style**
+
+We feel that a unified coding style is important, which is why we require a linter to
+be used. In this case **pep8** is used. Code must pass pep8's default tests.
+
+**Documentation**
+
+The script should be annotated using docstrings and comments where applicable
+
+## Contributing
+
+All active development is done on a [self-hosted Gitlab server](https://gitlab.namibsun.net).
+To contribute, send an email to hermann@krumreyh.com to create an account. Once you have an
+account, you may issue a merge or pull request.
+
+Using the Gitlab issue tracker is preferred, but the issues on Github are also
+taken into consideration.