update doc

README.md

@@ -11,6 +11,15 @@ $ git clone https://gitnet.fr/deblan/website-vacuum.git
 
 ## Usage
 
+Create a working directory:
+
+```
+$ mkdir example
+$ cd example
+```
+
+Then:
+
 ```bash
 $ ./bin/vacuum --help
 Usage: ./bin/vacuum [url] [filters] [-h|--help|--wget|--httrack]