Add Netty as a git submodule.

-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=81831533
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..bfd7c9c
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "lib/netty"]
+	path = lib/netty
+	url = https://github.com/netty/netty.git