Add CONTRIBUTING docs

[sdhutchins]

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[sdhutchins]

Contributing to this project

Thanks for your desire to contribute to this project.

Preparing your Fork

1. Hit 'fork' on Github, creating e.g. yourname/beRi.
2. Clone your project: git clone https://github.com/yourname/beRi.git.
3. Change to the project repository on your machine: cd beri
4. Create a branch: git checkout -b new-feature.

Development Mode Installation

Ensure that you have poetry installed (pip install --user poetry).

1. Change to the project repository on your machine: cd beri
2. Install in development mode: poetry install --develop beri

Making your Changes

1. Add your contributions
2. Run tests (use unittest) and make sure they pass.
3. Commit your changes: git commit -m "Added new feature" and please
   be descriptive with git commits!

Creating Pull Requests

1. Push your commit to get it back up to your fork: git push origin HEAD
2. Visit Github, click the handy "Pull request" button that it will
   make upon noticing your new branch.
3. In the description field, type the issue number (if submitting
   code fixing an existing issue) or describe the issue + your fix (if
   submitting a wholly new bugfix).
4. Hit 'submit' and ask for @datasnakes/snakeseq2018 to review!

[sdhutchins]

If anyone has input, please comment. We should add contributing docs to all of the projects. @datasnakes/snakeseq2018