Added note about APP_URL, closes #355

.env.example

@@ -3,7 +3,7 @@ APP_ENV=production
 APP_KEY=
 APP_DEBUG=false
 APP_LOG_LEVEL=debug
-# The URL of the AnonAddy instance, can be anything you like e.g. aa.example.com, or just example.com
+# The URL of the AnonAddy instance, can be anything you like e.g. https://aa.example.com, or just https://example.com, if using a non-standard port you must include it e.g. https://example.test:8000
 APP_URL=https://app.example.com
 
 LOG_CHANNEL=stack