Add MUSIC Distributed KV Store Documentation

This adds MUSIC Distributed KV store repo to doc.

Change-Id: Ib95f20f35cfb322e51a440fb2f49a9a432dd3ae3
Issue-ID: MUSIC-62
Signed-off-by: Shashank Kumar Shankar <shashank.kumar.shankar@intel.com>
diff --git a/.gitmodules b/.gitmodules
index 782cf51..2d774a9 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -308,3 +308,6 @@
 	url = ../externalapi/nbi
 	branch = .
 	ignore = dirty
+[submodule "docs/submodules/music/distributed-kv-store.git"]
+	path = docs/submodules/music/distributed-kv-store.git
+	url = ../music/distributed-kv-store