Unhardcode service user/group uid/gid values
Warn to not change cinder uid/gid values after user is created

Change-Id: Iff3e6491c14174c3aea12035878cc153b1621aef
diff --git a/README.rst b/README.rst
index 10c3c73..5bc4018 100644
--- a/README.rst
+++ b/README.rst
@@ -18,6 +18,8 @@
       controller:
         enabled: true
         version: juno
+        cinder_uid: 304
+        cinder_gid: 304
         default_volume_type: 7k2SaS
         availability_zone_fallback: True
         database:
@@ -61,6 +63,8 @@
       volume:
         enabled: true
         version: juno
+        cinder_uid: 304
+        cinder_gid: 304
         default_volume_type: 7k2SaS
         database:
           engine: mysql