User mention limit: clarify the error message?

[Moin]

@yrodiere

We could talk of Discourse automatically detecting source code and suggesting to format it

There is a theme-component doing that

Unformatted Code Detector

Summary Unformatted Code Detector detects unformatted code and gives a warning before posting. Preview Preview on theme-creator.discourse.org Repository Link https://github.com/discourse/unformatted-code-detector New to Discourse Themes? Beginner’s guide to using Discourse Themes Install this theme component Usage [Unformatted Code Detector] After installation, users posting unformatted code will see a warning mes…