(One of the authors here)

Make sure you read through the actual latest draft (especially section 6): https://tools.ietf.org/html/draft-foudil-securitytxt-11

Also, we are in the end stages of the IETF approval process so this should be official later this year (if all goes well): https://datatracker.ietf.org/doc/draft-foudil-securitytxt/