Sphinx doc for zuul {promote,show}

The Zuul client documentation was missing entries for the promote and
show sub commands.

Change-Id: Ia5501886984c8be2f900389bd65c166e093d416d
diff --git a/doc/source/client.rst b/doc/source/client.rst
index 1a843e5..5fe2252 100644
--- a/doc/source/client.rst
+++ b/doc/source/client.rst
@@ -31,3 +31,21 @@
   zuul enqueue --trigger gerrit --pipeline check --project example_project --change 12345,1
 
 Note that the format of change id is <number>,<patchset>.
+
+Promote
+^^^^^^^
+.. program-output:: zuul promote --help
+
+Example::
+
+  zuul promote --pipeline check --changes 12345,1 13336,3
+
+Note that the format of changes id is <number>,<patchset>.
+
+Show
+^^^^
+.. program-output:: zuul show --help
+
+Example::
+
+  zuul show running-jobs