Adding REDIS as backend for salt cache

The patch adds ability to configure REDIS as cache
backed for salt-master to be used as distibuted cache
further.

Change-Id: I62a29713c23ad3f591f6e937bfc5b13eba92f402
Related-PROD: PROD-20581
diff --git a/README.rst b/README.rst
index 5eecf1a..6263e43 100644
--- a/README.rst
+++ b/README.rst
@@ -438,6 +438,22 @@
                   nic01: AC:DE:48:AA:AA:AA
                   nic02: AC:DE:48:AA:AA:BB
 
+To enable Redis plugin for the Salt caching subsystem. The below pillar structure should be used
+
+.. code-block:: yaml
+
+  salt:
+    master:
+      cache:
+        plugin: redis
+        host: localhost
+        port: 6379
+        db: '0'
+        password: pass_word
+        bank_prefix: 'MCP'
+        bank_keys_prefix: 'MCPKEY'
+        key_prefix: 'KEY'
+        separator: '@'
 
 
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