docs(video): finalize for a live on-camera payment

Owner chose to record a real mainnet payment. Two changes so the video and the
repo stay honest afterward:

- The narration said "Seven mainnet transactions." A live payment adds an
  eighth to strk20.json, which would make the spoken count stale the moment the
  hash lands. It is now count-free: "Real mainnet transactions, all verified."

- The shot list now calls for a FRESH receive address, never paid before. That
  makes this the first genuine end-to-end payment to a merchant address, which
  is the one thing the earlier seven do not show, and the after-steps update the
  README's honest caveat and re-run the claims checker.