Mention VeriFast build attestation

Author: btj

.github/workflows/verifast.yml

@@ -28,6 +28,7 @@ jobs:
         run: |
           cd ~
           curl -OL https://github.com/verifast/verifast/releases/download/24.12/verifast-24.12-linux.tar.gz
+          # https://github.com/verifast/verifast/attestations/3689894
           echo '51bebf990f31666abcd3675000e7714ef79b417390e930953ef25383e8d59421  verifast-24.12-linux.tar.gz' | shasum -a 256 -c
           tar xf verifast-24.12-linux.tar.gz