Document jobs

Add inline documentation to jobs and render it in the jobs doc page.
Adjust the roles page to match jobs for title and filename.

Change-Id: I47a2b4b379c8517b0dea59a75943f3f871c29046
diff --git a/doc/source/index.rst b/doc/source/index.rst
index 9254c23..4c53203 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -139,7 +139,8 @@
 Enable :doc:`devstack plugins <plugins>` to support additional
 services, features, and configuration not present in base devstack.
 
-Use devstack in your CI with :doc:`Ansible roles <roles>` for Zuul V3.
+Use devstack in your CI with :doc:`Ansible roles <zuul_roles>` and
+:doc:`Jobs <zuul_jobs>` for Zuul V3.
 
 Get :doc:`the big picture <overview>` of what we are trying to do
 with devstack, and help us by :doc:`contributing to the project