Update README.rst for X.509 auth for MySQL and Designate

Related-PROD: PROD-22737

Change-Id: Ibddba4f477abd10bd67c4cb253bcc57e9487261f
diff --git a/README.rst b/README.rst
index 2ba22ba..990e84d 100644
--- a/README.rst
+++ b/README.rst
@@ -198,6 +198,29 @@
 
     dig @127.0.0.1 test.example.com.
 
+Enable x509 and ssl communication between Designate and Galera cluster.
+---------------------
+By default communication between Designate and Galera is unsecure.
+
+designate:
+  server:
+    database:
+      x509:
+        enabled: True
+
+You able to set custom certificates in pillar:
+
+designate:
+  server:
+    database:
+      x509:
+        cacert: (certificate content)
+        cert: (certificate content)
+        key: (certificate content)
+
+You can read more about it here:
+    https://docs.openstack.org/security-guide/databases/database-access-control.html
+
 Documentation and Bugs
 ======================