98ce46c009 Update docs on witness_mut (Tobin C. Harding)
Pull request description:
Recently during the rust-bitcoin workshop at TABConf devs were thrown off by the example on `witness_mut`. We have some work going on to add examples and a cookbook that all demonstrate usage of `witness_mut`.
Remove the docs on `witness_mut` and direct devs to the `examples/sign-tx-*` files.
ACKs for top commit:
apoelstra:
ACK 98ce46c009
Kixunil:
ACK 98ce46c009
Tree-SHA512: e662213db4cbdaa53f6927cc1b10c1b6276f538cc6ad0d4bfff6dfcbf042f287a14bf5bfc88eeba7a32646c3d6741c5e09d11bb76666572a12a2043db55a2f38