Merge bitcoindevkit/bdk#1288: doc(esplora): fix broken link in README

Merge bitcoindevkit/bdk#1288: doc(esplora): fix broken link in README

7c0f4653b281b4288e92ed8cd45ead8abd104f52 doc(esplora): fix broken link in README (vmammal)

Pull request description:

  ### 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:
  danielabrozzoni:
    ACK 7c0f4653b281b4288e92ed8cd45ead8abd104f52

Tree-SHA512: 6e09a0b74c1a64bc9d0d0a067daf7766c4a46511c22b676251f61608d770d3ea2c1df81d4e9bbbee69720cad5cd2deb9b146cb7751277871f0cbf1be96efcc9f