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/zuul_roles.rst b/doc/source/zuul_roles.rst
new file mode 100644
index 0000000..4939281
--- /dev/null
+++ b/doc/source/zuul_roles.rst
@@ -0,0 +1,4 @@
+Zuul CI Roles
+=============
+
+.. zuul:autoroles::