Add doc submodule for MSB discovery

Change-Id: I6a9aea98c0989bdc3363c8f434138daaaa20846b
Issue-Id: MSB-80
Signed-off-by: HuabingZhao <zhao.huabing@zte.com.cn>
diff --git a/.gitmodules b/.gitmodules
index 1629c0c..5719b92 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -71,3 +71,6 @@
 [submodule "docs/submodules/msb/apigateway.git"]
 	path = docs/submodules/msb/apigateway.git
 	url = ../msb/apigateway
+[submodule "docs/submodules/msb/discovery.git"]
+	path = docs/submodules/msb/discovery.git
+	url = ../msb/discovery