docs: better docs, mv doxygen to sphinx

This patch refactors the VPP sphinx docs
in order to make it easier to consume
for external readers as well as VPP developers.

It also makes sphinx the single source
of documentation, which simplifies maintenance
and operation.

Most important updates are:

- reformat the existing documentation as rst
- split RELEASE.md and move it into separate rst files
- remove section 'events'
- remove section 'archive'
- remove section 'related projects'
- remove section 'feature by release'
- remove section 'Various links'
- make (Configuration reference, CLI docs,
  developer docs) top level items in the list
- move 'Use Cases' as part of 'About VPP'
- move 'Troubleshooting' as part of 'Getting Started'
- move test framework docs into 'Developer Documentation'
- add a 'Contributing' section for gerrit,
  docs and other contributer related infos
- deprecate doxygen and test-docs targets
- redirect the "make doxygen" target to "make docs"

Type: refactor

Change-Id: I552a5645d5b7964d547f99b1336e2ac24e7c209f
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/docs/contributing/writingdocs.rst b/docs/contributing/writingdocs.rst
new file mode 100644
index 0000000..ba37130
--- /dev/null
+++ b/docs/contributing/writingdocs.rst
@@ -0,0 +1,52 @@
+.. _buildingrst:
+
+Writing VPP Documentation
+=========================
+
+These instructions show how the VPP documentation sources are built.
+
+The VPP Documents are written using `reStructuredText <http://www.sphinx-doc.org/en/master/usage/restructuredtext/index.html>`_ (rst),
+or markdown (md). These files are then built using the Sphinx build system `Sphinx <http://www.sphinx-doc.org/en/master/>`_.
+
+Building the docs
+-----------------
+
+Start with a clone of the vpp repository.
+
+.. code-block:: console
+
+   $ git clone https://gerrit.fd.io/r/vpp
+   $ cd vpp
+
+Build the html **index.html** file:
+
+.. code-block:: console
+
+   $ make docs
+
+Delete all the generated files with the following:
+
+.. code-block:: console
+
+   $ make docs-clean
+
+View the results
+----------------
+
+If there are no errors during the build process, you should now have an ``index.html`` file in your ``vpp/docs/_build/html`` directory, which you can then view in your browser.
+
+Whenever you make changes to your ``.rst`` files that you want to see, repeat this build process.
+
+Writing Docs and merging
+------------------------
+
+Documentation should be added as ``.rst`` file in the ``./src/`` tree next to the code it refers to. A symlink should be added at the relevant place in the ``./docs`` folder and a link in the appropriate place in the tree.
+
+To ensure documentation is correctly inserted, you can run
+
+.. code-block:: console
+
+   $ ./extras/scripts/check_documentation.sh
+
+VPP documents are reviewed and merged like and other source code. Refer to :ref:`gitreview`
+to get your changes reviewed and merged.