update readme

README.md

@@ -22,13 +22,19 @@ open http://localhost:7878
 
 and you will be redirected to `REDIRECT_URL` from your env.
 
-## Configuration
+### Configuration
 
 It loads configuration from environment variables:
 
-- `REDIRECT_URL`: the url to redirect to
+- `REDIRECT_URL`: (**required**) the url to redirect to
 - `PERMANENT`: if true, it will return a 301 status code, otherwise 302
 
+## Docker example
+
+```
+docker run -p 7878:7878 -e REDIRECT_URL=https://nzambello.dev -e PERMANENT=true nzambello/redirector:latest
+```
+
 ## Docker compose example
 
 ```yaml