docs(tip-0001): add tempo transaction spec (#3808)

Adds TIP-0001 by copying the existing Tempo Transactions spec into the
repo as a retroactive TIP.

Tempo Transactions shipped at genesis and are already live on mainnet,
so this PR makes the existing spec discoverable alongside the rest of
the TIP set. It also points readers to the related follow-on transaction
TIPs: TIP-1007, TIP-1009, TIP-1011, and TIP-1020.

Author: legion2002