Add docs build jobs

Start with building Sphinx, include links to the anticipated locations
for /releasenotes and /specs.

Change-Id: I111e4dfc2a31a97b869df25e0d059b8423d25d6a
Signed-off-by: Dean Troyer <dtroyer@gmail.com>

.zuul.yaml

@@ -1,5 +1,7 @@
 ---
 - project:
+    templates:
+      - build-openstack-sphinx-docs-python3
     check:
       jobs:
         - openstack-tox-linters

doc/source/contributing.rst

@@ -1,5 +0,0 @@
-============
-Contributing
-============
-
-The contributing page.

doc/source/contributor/index.rst

@@ -0,0 +1,8 @@
+=========================
+Contributor Documentation
+=========================
+
+The contributing page.
+
+.. toctree::
+   :maxdepth: 1

doc/source/index.rst

@@ -15,7 +15,23 @@ Contents
    :caption: Contents:
 
    getting_started.rst
-   contributing.rst
+   contributor/index
+
+Release Notes
+-------------
+
+.. toctree::
+   :maxdepth: 1
+
+   Release Notes <http://docs.starlingx.io/releasenotes>
+
+Specs
+-----
+
+.. toctree::
+   :maxdepth: 1
+
+   Release Notes <http://docs.starlingx.io/specs>
 
 Indices and tables
 ==================