bootstrap: enable tidy auto extra checks on tools profile

bootstrap.example.toml

@@ -475,6 +475,9 @@
 # Note that if any value is manually given to bootstrap such as
 # `./x test tidy --extra-checks=js`, this value is ignored.
 # Use `--extra-checks=''` to temporarily disable all extra checks.
+#
+# Automatically enabled in the "tools" profile.
+# Set to the empty string to force disable (recommeded for hdd systems).
 #build.tidy-extra-checks = ""
 
 # Indicates whether ccache is used when building certain artifacts (e.g. LLVM).