Document a release process

Author: adamtheturtle

CONTRIBUTING.rst

@@ -0,0 +1,21 @@
+Contributing
+============
+
+Release process
+---------------
+
+* Update the CHANGELOG on the master branch
+* Update ``__version__`` in ``pip_check_reqs/__init__.py`` on the master branch.
+
+Run the following steps:
+
+.. code:: sh
+
+   git checkout master && \
+   git pull && \
+   pip install twine && \
+   pip install -r requirements.txt && \
+   rm -rf build dist && \
+   git status # There should be no uncommitted changes.  && \
+   python setup.py sdist bdist_wheel  && \
+   twine upload -r pypi dist/*