Update initialize command. Issue #192

Author: shakaran

README.md

@@ -49,6 +49,12 @@ public function registerBundles()
 }
 ```
 
+If you use 2.x branch or dev-master version of this bundle you need additionally:
+
+```bash
+php bin/console avanzu:admin:initialize
+```
+
 Install assets (preferably using symlink method but hardcopy works as well)...
 
 ```bash