Add doc submodule for MSB java sdk

Change-Id: I95842c02959ee19d60c43248ddd56284b716cd69
Issue-Id: MSB-81
Signed-off-by: HuabingZhao <zhao.huabing@zte.com.cn>
diff --git a/.gitmodules b/.gitmodules
index 5719b92..4bdb2c0 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -74,3 +74,6 @@
 [submodule "docs/submodules/msb/discovery.git"]
 	path = docs/submodules/msb/discovery.git
 	url = ../msb/discovery
+[submodule "docs/submodules/msb/java-sdk.git"]
+	path = docs/submodules/msb/java-sdk.git
+	url = ../msb/java-sdk