Merge bitcoindevkit/bdk#1884: doc: remove persist crate from README

Merge bitcoindevkit/bdk#1884: doc: remove persist crate from README

7b8faa3b31de91d1bfc46f5020b79eea6eed0cbb doc: remove persist crate from README (Luis Schwab)

Pull request description:

  <!-- You can erase any parts of this template not applicable to your Pull Request. -->

  ### Description

  - Removed `persist` crate from `README.md`

  ### Checklists

  #### All Submissions:

  * [X] I've signed all my commits
  * [X] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [X] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  LagginTimes:
    ACK 7b8faa3b31de91d1bfc46f5020b79eea6eed0cbb
  ValuedMammal:
    ACK 7b8faa3b31de91d1bfc46f5020b79eea6eed0cbb

Tree-SHA512: d15ab9a5b7002e71790324d02c1650bc15a8e6c28c16d0cbe04cfd0d610f93a322abd00f5aaf25416d0055c3008c46079f5effefeb66ff6dd5e6e770bbf3735b