Docs: be more explicit regarding oslo_limit.endpoint_id

Make sure readers understand where this id comes from.

Change-Id: I2b6425f8a2bce4e47ebb15f4161fa238b3b6c6f9
Closes-Bug: #2059829
(cherry picked from commit 70d18c8)

Author: CyrilRoelandteNovance

doc/source/install/configure-quotas.rst

@@ -9,14 +9,24 @@
      username = glance
      system_scope = all
      password = GLANCE_PASS
-     endpoint_id = 340be3625e9b4239a6415d034e98aace
+     endpoint_id = ENDPOINT_ID
      region_name = RegionOne
 
   .. end
 
   Replace ``GLANCE_PASS`` with the password you chose for the
   ``glance`` user in the Identity service.
 
+  Replace ENDPOINT_ID with the ID of the image endpoint you
+  created earlier (in our case, this would be
+  340be3625e9b4239a6415d034e98aace), and that you may find by running:
+
+  .. code-block:: console
+
+    $ openstack endpoint list --service glance --region RegionOne
+
+  .. end
+
   Make sure that the glance account has reader access to
   system-scope resources (like limits):