upd README about compile front

README.md

@@ -123,6 +123,16 @@ docker-compose exec citizen-front bash
 root@9c0fea7720a0:/home/appuser/citizen/frontend# npm run ng serve -- --host 0.0.0.0 --port 4200 --configuration=fr --poll 2000
 ```
 
+But note that for persistently-built frontend files, you must run:
+
+```bash
+docker-compose exec citizen-front bash
+root@9c0fea7720a0:/home/appuser/citizen/frontend# npm run build:i18n-ssr
+```
+
+or `npm run build:fr` for speeding up. 
+
+
 ## Deploiement sur un serveur distant