Clarify that BitTorrent verification doesn't replace OpenPGP verification

Your BitTorrent client verifies your download automatically based on a cryptographic checksum in the Torrent file.

but users should verify the downloaded iso using gpg. we should make clear that these are different kinds of verification.

Feature Branch: web/11019-bittorrent-openpgp

Original created by @muri on 11019 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information