Merge bitcoindevkit/bdk#1039: docs: add required style for commit messages

e17f03e7555b7b6f5348b9854f3d4ef559e84d75 docs: add required style for commit messages (Steve Myers)

Pull request description:

  ### Description

  Update CONTRIBUTING.md to specify that new commits should use 'Conventional Commits 1.0' style messages. See https://www.conventionalcommits.org/en/v1.0.0/.  I also fixed our current MSRV in the doc and fixed a spelling error.

  ### Notes to the reviewers

  I'm open to suggestions if anyone has another well documented style for commit messages.

  ### Changelog notice

  None.

  ### 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:
  thunderbiscuit:
    ACK e17f03e7555b7b6f5348b9854f3d4ef559e84d75. I've been using conventional commits for Padawan for over 2 years and think it's got good value, particularly on projects with bigger teams and number of contributors.
  danielabrozzoni:
    ACK e17f03e7555b7b6f5348b9854f3d4ef559e84d75 - I was hesitant at first, but I think this would make the commit messages cleaner (and in most cases even shorter). Going forward we should consider adding a CI check enforcing this.

Tree-SHA512: 5f4c42814e35e013ff7846110b2897a35720b8f4b8974f8c8004fc0f5161a10076cac62a7aa711c14295129999f93e238034972f28b77145c1917613f8856b03