Add additional zuul.conf information

Change-Id: I78c7b4adbcc6967f22d7839808e55314275f74db
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>
diff --git a/doc/source/zuul.rst b/doc/source/zuul.rst
index d8d72e6..563aa23 100644
--- a/doc/source/zuul.rst
+++ b/doc/source/zuul.rst
@@ -10,11 +10,11 @@
 
 **zuul.conf**
   Connection information for Gerrit and Gearman, locations of the
-  other config files.
+  other config files. (required)
 **layout.yaml**
-  Project and pipeline configuration -- what Zuul does.
+  Project and pipeline configuration -- what Zuul does. (required)
 **logging.conf**
-    Python logging config.
+    Python logging config. (optional)
 
 Examples of each of the three files can be found in the etc/ directory
 of the source distribution.
@@ -41,17 +41,23 @@
 gearman
 """""""
 
+Client connection information for gearman. If using Zuul's builtin gearmand
+server just set **server** to 127.0.0.1.
+
 **server**
   Hostname or IP address of the Gearman server.
-  ``server=gearman.example.com``
+  ``server=gearman.example.com`` (required)
 
 **port**
   Port on which the Gearman server is listening.
-  ``port=4730``
+  ``port=4730`` (optional)
 
 gearman_server
 """"""""""""""
 
+The builtin gearman server. Zuul can fork a gearman process from itself rather
+than connecting to an external one.
+
 **start**
   Whether to start the internal Gearman server (default: False).
   ``start=true``
@@ -67,6 +73,11 @@
 zuul
 """"
 
+Zuul's main configuration section. At minimum zuul must be able to find
+layout.yaml to be useful.
+
+.. note:: Must be provided when running zuul-server
+
 .. _layout_config:
 
 **layout_config**
@@ -118,6 +129,13 @@
 merger
 """"""
 
+The zuul-merger process configuration. Detailed documentation on this process
+can be found on the :doc:`merger` page.
+
+.. note:: Must be provided when running zuul-merger. Both services may share the
+          same configuration (and even host) or otherwise have an individual
+          zuul.conf.
+
 **git_dir**
   Directory that Zuul should clone local git repositories to.
   ``git_dir=/var/lib/zuul/git``