Add doc submodule for usecase-ui

Change-Id: I24d1254cf2924df46d394a06b68470b3f814c130
Issue-Id: USECASEUI-48
Signed-off-by: shentao <shentao@chinamobile.com>
diff --git a/.gitmodules b/.gitmodules
index 4381623..5ba9b96 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -252,3 +252,6 @@
 [submodule "docs/submodules/vid/asdcclient.git"]
 	path = docs/submodules/vid/asdcclient.git
 	url = ../vid/asdcclient
+[submodule "docs/submodules/usecase-ui.git"]
+	path = docs/submodules/usecase-ui.git
+	url = ../usecase-ui