Update PMB_README.md

PMB_README.md

@@ -35,7 +35,7 @@ Then:
     docker-compose up -d
 
 Note: docker-compose down && docker-compose up are necessary. "restart" will not reload .env\
-Note: username can be anything configured as account in protonmail web interface.
+Note: username can be anything setup as account in protonmail web. Identity and addresses -> my addresses.
 
 ## msmtp test