readme: add --interface argument

Signed-off-by: Francesco Pham <francesco.pham@huawei.com>

README.md

@@ -45,7 +45,7 @@ $ pip3 install -r requirements.txt
 
 Run resource directory:
 ```console
-$ python3 src/resource_directory.py
+$ python3 src/resource_directory.py --interface <name of the network interface>
 ```
 
 Run the example Eddie endpoint: