text: Title: Mention log.html if long message is cut
  Body: Relevant error messages may be hidden by Robot if the output is verbose. The current warning is `[ Message content over the limit has been removed. ]`, but it's not obvious that Robot does actually preserve the full output in log.html. I think it would be helpful to change the warning to something like `[ Message content over the limit has been removed, see log.html for the full output. ]`
  
  I can make a PR to fix this, just wanted to make an issue first in case there are concerns.