Merge bitcoindevkit/bdk-cli#190: chore: update README rust version badge to 1.75.0

Merge bitcoindevkit/bdk-cli#190: chore: update README rust version badge to 1.75.0

0103e4be1705804e1a74d68bb5c57aafa200f0c4 chore: update README rust version badge to 1.75.0 (Steve Myers)

Pull request description:

  ### Description

  Update README rust version badge to 1.75.0.

  ### Notes to the reviewers

  I forgot to do this on the last release.

  ### Checklists

  #### All Submissions:

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

ACKs for top commit:
  tvpeter:
    ACK 0103e4be1705804e1a74d68bb5c57aafa200f0c4

Tree-SHA512: cf6707e837cdeceb1c15ffd8170106b627f38e41bf0044ae196c99d4ebd529f27d3b17f8413e574ed361ae29d8906e20a8cadfd07fce6129942b1fd6eb0c389b