fix(compose.yml): add sample extra_hosts for simplicity

README.md

@@ -163,10 +163,10 @@ PUT /{page}/
 ```
 
 ```bash
-# create /my-website/ that proxies to http://localhost:8000
+# create /my-website/ that proxies to http://host.containers.internal:8000
 curl -X PUT \
   -H 'X-Token: <TOKEN>' \
-  -H 'X-Proxy: http://localhost:8000' \
+  -H 'X-Proxy: http://host.containers.internal:8000' \
   https://stapler-host/my-project/
 ```