Doctor suggest git clean -f if unstaged files

This is safe, I tested various scenarios, including Homebrew installed in ~. The only files that are removed are unexpected files in Homebrew's already managed directories.

Library/Homebrew/cmd/doctor.rb

@@ -788,7 +788,7 @@ def check_git_status
       If this a surprise to you, then you should stash these modifications.
       Stashing returns Homebrew to a pristine state but can be undone
       should you later need to do so for some reason.
-          cd #{HOMEBREW_REPOSITORY} && git stash
+          cd #{HOMEBREW_REPOSITORY}/Library && git stash && git clean -f
       EOS
     end
   end