Fix up README.md in tools/update-responses

While reviewing the fix for #33274 (closed) I realized that we might want to go over our 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.