Password must be a minimum of 6 characters - this should be added to documentation

[dmo9]

I'm locally hosting & this is my first time using docker.

Spent a good few hours pulling my hair out because I followed the directions exactly but the page simply would not load (saying no data had been transferred). Eventually, after running sudo docker-compose logs I realized the problem was that my password in plausible-conf.env was not at least 6 characters.