add doc on exit_chat

README.md

@@ -15,7 +15,7 @@ in two modes:
 * command mode (blue bottom bar)
 * chat mode    (green bottom bar)
 
-commands in chat mode are called by prepending `/` so a `/back` brings you back to command mode
+commands in chat mode are called by prepending `/` so a `/back` or `/exit_chat` brings you back to command mode
 
 commands are autocompleted thanks to the amazing prompt_toolkit package