Hint for admin users variable

Running a self-host environment I was curious about what more I can do as an admin. Even though the ADMIN_USERS variable is described in general I couldn’t find a hint what exactly to provide and where to find it. I first tried the registered email address, but it is actually the username shown in household without the “@-sign”. It might be worth to add a hint to the .env file and/or docs, although the practical value of being an admin is currently fairly modest.