Fix documentation build
The contributing.rst file was referencing a non-existing path, and
index.rst referenced a non-existing usage.rst file.
Added build-openstack-sphinx-docs job to test doc changes
Change-Id: Ie08e6b1a49a69fedb0fe1ddcf0225d0018aa65b4
diff --git a/doc/source/contributing.rst b/doc/source/contributing.rst
index 2aa0707..1728a61 100644
--- a/doc/source/contributing.rst
+++ b/doc/source/contributing.rst
@@ -1,4 +1,4 @@
============
Contributing
============
-.. include:: ../../../CONTRIBUTING.rst
+.. include:: ../../CONTRIBUTING.rst