fix explanation for ratings wrt the old 5-star lab

[simon-weber]

Sourced from this mailing list post:

Took me a while to realize that if you used the 5 star system prior to it going away the 5=thumbs up and 1=thumbs down doesn't hold true. I.e. I have 1-5 in the mix. Might be worth updating the notes as I thought it wasn't working.