DOCUMENT: New bitcoin script use cases for LBTCftCL

[ChristopherA]

Document new weird transactions like blocking transactions, vaults, covenants, etc. and decide when appropriate to publish in course.

• Revault: https://github.com/revault/practical-revault
• Delegated Signatures https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-March/018615.html