updated README

README.md

@@ -14,3 +14,9 @@ run the image with ```docker compose run -it --rm gentoo```.  If you want
 the image to persist a while, you could start it with ```docker compose run -d --rm --name gentoo gentoo tail -f /dev/null```,
 do what you need within it with ```docker exec -it gentoo bash```, and dispose
 of it with ```docker stop gentoo```.
+
+One-line update and run:
+
+```
+docker compose build && docker compose run -d --rm --name gentoo gentoo tail -f /dev/null && screen -dmS gentoo docker exec -it gentoo bash && sleep 2 && screen -dr gentoo
+```