Expand contributor documentation

- Move from CONTRIBUTING.md to a subdirectory in docs, so
  we can expand and add more documentation.
- Move from markdown to reStructuredTest
- Add a direct blurb in the JupyterHub docs index page on
  how contribution.
- More prominent link to the Code of Conduct
- Add section on getting in touch with the JupyterHub community

docs/source/contributing/docs.rst

@@ -0,0 +1,49 @@
+.. _contributing/docs:
+
+==========================
+Contributing Documentation
+==========================
+
+Documentation is often more important than code. This page helps
+you get set up on how to contribute documentation to JupyterHub.
+
+Building documentation locally
+==============================
+
+
+We use `sphinx <http://sphinx-doc.org>`_ to build our documentation. It takes
+our documentation source files (written in `markdown
+<https://daringfireball.net/projects/markdown/>`_ or `reStructuredText
+<http://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html>`_ &
+stored under the ``docs/source`` directory) and converts it into various
+formats for people to read. To make sure the documentation you write or
+change renders correctly, it is good practice to test it locally.
+
+#. Make sure you have successfuly completed :ref:`contributing/setup`.
+
+#. Install the packages required to build the docs.
+
+   .. code-block:: bash
+
+      pip install -r docs/requirements.txt
+
+#. Build the html version of the docs. This is the most commonly used
+   output format, so verifying it renders as you should is usually good
+   enough.
+
+   .. code-block:: bash
+
+      cd docs
+      make html
+
+   This step will display any syntax or formatting errors in the documentation,
+   along with the filename / line number in which they occurred. Fix them,
+   and re-run the ``make html`` command to re-render the documentation.
+
+#. View the rendered documentation by opening ``build/html/index.html`` in 
+   a web browser. 
+
+   .. tip::
+
+      On macOS, you can open a file from the terminal with ``open <path-to-file>``.
+      On Linux, you can do the same with ``xdg-open <path-to-file>``.