Fix readme for multi-node setup

The readme currently states that a compute node in a multi-node setup
requires the glance-api service to be enabled. But actually
the glance-api service is only required on the controller node where
glance-registry is running.
Running the glance-api service on a node without glance-registry will
even lead to a failure of glance-api, as the glance cache directory
will not be created without enabling glance-registry.

Change-Id: Ie92533f3333f3fe3e2d747762e60f2f42a233e79
Closes-bug: #1441198
diff --git a/README.md b/README.md
index 53de970..faf2d93 100644
--- a/README.md
+++ b/README.md
@@ -333,7 +333,7 @@
 You can then run many compute nodes, each of which should have a `stackrc`
 which includes the following, with the IP address of the above controller node:
 
-    ENABLED_SERVICES=n-cpu,rabbit,g-api,neutron,q-agt
+    ENABLED_SERVICES=n-cpu,rabbit,neutron,q-agt
     SERVICE_HOST=[IP of controller node]
     MYSQL_HOST=$SERVICE_HOST
     RABBIT_HOST=$SERVICE_HOST