Write a new documentation page with branch info

This is related to #1352.

Once this PR is merged we should:

- Change github default branch to `dev`
- Delete `master`
- Confirm that read the docs is looking at `release`

Am I missing anything?

We should also remove the release process information from the wiki
(assuming we're happy with what I've written here).

Finally, once #1360 is done we should make sure we update the docs with
the relevant information.

Author: drvinceknight

docs/tutorials/contributing/index.rst

@@ -10,6 +10,7 @@ Contents:
    :maxdepth: 2
 
    guidelines.rst
+   setting_up_the_environment.rst
    strategy/index.rst
    library/index.rst
    running_tests.rst

docs/tutorials/contributing/setting_up_the_environment.rst

@@ -0,0 +1,32 @@
+Setting up the environment
+==========================
+
+Installing all dependencies
+---------------------------
+
+All testing dependencies can be installed by running::
+
+  $ pip install -r requirements.txt
+
+It is recommended to do this using a virtual environment tool of your choice.
+
+The git workflow
+----------------
+
+There are two important branches in this repository:
+
+- :code:`dev`: The most up to date branch with no failing tests.
+  This is the default branch on github.
+- :code:`release`: The latest release.
+
+When working on a new contribution branch from the latest :code:`dev` branch and
+open a Pull Request on github from your branch to the :code:`dev` branch.
+
+The procedure for a new release (this is carried out by one of core maintainers):
+
+1. Create a Pull Request from :code:`dev` to :code:`release` which should
+   include an update to :code:`axelrod/version.py` and :code:`CHANGES.md`
+2. Create a git tag.
+3. Push to github.
+4. Create a release on github.
+5. Push to PyPi: :code:`python setup.py sdist bdist_wheel upload`