[Disk] Added parametrization of disk_allocation_ratio.

Change-Id: Icc734e213bf4f3f94defc7b10f68914cfa86a3b6
diff --git a/README.rst b/README.rst
index 5bd2abc..152d9a7 100644
--- a/README.rst
+++ b/README.rst
@@ -22,6 +22,7 @@
         security_group: true
         cpu_allocation_ratio: 8.0
         ram_allocation_ratio: 1.0
+        disk_allocation_ratio: 1.0
         bind:
           public_address: 10.0.0.122
           public_name: openstack.domain.com