Docs: mention valid characters that need to be supported for scoreboard display

[matt (gingerbeardman)]

It would be great if the scoreboard API docs page could mention the range of valid characters that need to be supported.

Scoreboard API - Playdate Help

Somebody on Fore! Track leaderboards has an underscore character in their name, which was a surprise.

The playdate account says when you try to enter invalid characters:
"Enter a valid username. This value may contain only English letters, numbers, and @/./+/-/_ characters.”

Thanks to @stuffbyrae for help with this

[dave (Dave Hayden)]

Just leaving a quick note here that this is in the tracker. One of these days I'll sit down and do all of the documentation fixes in one go.