Add device-management-interface documentation

Change-Id: I01f58e3d1cd8cd968e995bb912f14c0937034408
diff --git a/git_refs b/git_refs
index f81e56e..0063114 100644
--- a/git_refs
+++ b/git_refs
@@ -11,16 +11,17 @@
 
 _REPO NAME_             _DIR_    _REF_
 
-bbsim                      /        master
-cord-tester                /        master
-ofagent-go                 /        master
-openolt                    /        master
-pyvoltha                   /        master
-voltctl                    /        master
-voltha-go                  /        master
-voltha-openolt-adapter     /        master
-voltha-openonu-adapter     /        master
-voltha-openonu-adapter-go  /        master
-voltha-protos              /        master
-voltha-system-tests        /        master
-kind-voltha                /        master
+bbsim                        /        master
+cord-tester                  /        master
+ofagent-go                   /        master
+openolt                      /        master
+pyvoltha                     /        master
+voltctl                      /        master
+voltha-go                    /        master
+voltha-openolt-adapter       /        master
+voltha-openonu-adapter       /        master
+voltha-openonu-adapter-go    /        master
+voltha-protos                /        master
+voltha-system-tests          /        master
+kind-voltha                  /        master
+device-management-interface  /        master