Add contribution guide

# 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.