edit readme

README.md

@@ -1,6 +1,7 @@
 # Simple Todo list
 
 This is a simple todo list, written in javascript, using express for the backend and react/redux for the frontend.
+It also can work in offline, thanks to redux-offline.
 
 ## Running it
 
@@ -13,3 +14,19 @@ And visit it at http://localhost:3000
 ## Configuration
 
 By default development server uses mongodb todolist database at localhost, you can change it with environment variable `DEV_DB_URI`
+
+If you are running it in production environment, you should set these environment variables:
+
+```
+HSTS = true/false
+MONGODB_URI
+PORT
+SECRET
+```
+
+## Offline
+
+To enable service worker, the frontend should be run in production environment.
+To run it locally you should build the frontend: `cd react && npm run build`.
+
+And visit it at http://localhost:4000