Enable sphinx on servers_client

servers_client is most useful client for testing, but the docstring was
not enabled on the site. So this patch makes it enabled.

Change-Id: I031de923deab74bc0f84cff52f470ab233b7dbba
diff --git a/doc/source/library/clients.rst b/doc/source/library/clients.rst
index 086cfc9..0f4ba4c 100644
--- a/doc/source/library/clients.rst
+++ b/doc/source/library/clients.rst
@@ -16,9 +16,18 @@
 The ``ServiceClients`` class provides a convenient way to get access to all
 available service clients initialized with a provided set of credentials.
 
-------------------
-The clients module
-------------------
+-----------------------------
+The clients management module
+-----------------------------
 
 .. automodule:: tempest.lib.services.clients
    :members:
+
+------------------------------
+Compute service client modules
+------------------------------
+
+.. toctree::
+   :maxdepth: 2
+
+   service_clients/compute_clients