Updated readme.md with heroku app update steps

Author: soygul

Diff for: readme.md

@@ -99,6 +99,12 @@ Example:
 yo angular-fullstack:deploy heroku
 ```
 
+After app modifications run:
+```bash
+grunt heroku
+```
+then commit and push the heroku folder.
+
 ### Route
 Generates a controller and view, and configures a route in `app/scripts/app.js` connecting them.