docs: new branch expension of nwjs app

Author: rhiokim

Diff for: README.md

@@ -59,6 +59,7 @@ $ npm run docker        // run build, rm, run at once
 ```
 master
   \_ nw
+    \_ nw-ext (offline first app with pouchdb, etc)
   \_ material
   \_ ant-design
   \_ photon