Suggest users to clean working directory when Nailgun server failed

[lwronski]

Fixes #1882.

I reproduced bug from #1882, and now when users run scala-cli it print the following error:

➜  scala-demo /Users/lwronski/projects/scala-cli/out/cli/standaloneLauncher.dest/launcher Hello.scala 
[E] Failed to load project from /private/tmp/scala-demo/.scala-build/.bloop/project_853f6d1dbb-25fccf1679.json
Something is wrong with the current configuration. Nailgun server failed with exit code 1.
To resolve the problem, please run the clean sub-command to clear the working directory and remove caches.
If the error persists, please report the issue as a bug and attach a log with increased verbosity by passing -v -v -v.
Error: java.lang.RuntimeException: Bloop BSP connection in /Users/lwronski/Library/Caches/ScalaCli/bsp-sockets/proc-91655 was unexpectedly closed or bloop didn't start.
For more details, please see '/private/tmp/scala-demo/.scala-build/stacktraces/1678358545-18379785233871606763.log'

[alexarchambault]

Apart from the minor extra suggested change, LGTM