Fix up README.md in tools/update-responses
While reviewing the fix for #33274 (closed) I realized that we might want to go
README.md file, too, and improving it where needed.
E.g. there is a
config.yml mentioned which I did not find, I think,
and some typos, e.g.:
"for Tor Browser updater" -> "for the Tor Browser updater" or
"correspo" and "ndance" on a new line.