doc(readme): add Web Interface wiki link

README.md

@@ -101,3 +101,4 @@ another computer.
 
 * [User Management](https://github.com/cad/ovpm/wiki/User-Management)
 * [Network Management](https://github.com/cad/ovpm/wiki/Network-Management)
+* [Web Interface](https://github.com/cad/ovpm/wiki/Web-Interface)