README.rst updated

Change-Id: I54d19f921fd4a3b7f7477400b801bcc92b8aefd9
diff --git a/README.rst b/README.rst
index 73c515a..dc1fd5a 100644
--- a/README.rst
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@@ -18,6 +18,10 @@
 Sample pillars
 ==============
 
+.. caution:: 
+
+    When you use localhost as your database host (keystone:server:database:host), sqlalchemy will try to connect to /var/run/mysql/mysqld.sock, may cause issues if you located your mysql socket elsewhere
+
 Full stacked keystone
 
 .. code-block:: yaml