Add doc submodule for MSB api gateway

Change-Id: I793c45c571d83426d701e00f476768cc870a4dda
Issue-Id: MSB-79
Signed-off-by: HuabingZhao <zhao.huabing@zte.com.cn>
diff --git a/.gitmodules b/.gitmodules
index bffedcf..1629c0c 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -68,3 +68,6 @@
 [submodule "docs/submodules/vfc/nfvo/lcm.git"]
 	path = docs/submodules/vfc/nfvo/lcm.git
 	url = ../vfc/nfvo/lcm
+[submodule "docs/submodules/msb/apigateway.git"]
+	path = docs/submodules/msb/apigateway.git
+	url = ../msb/apigateway