Merge bitcoindevkit/bdk#738: Fix docs.rs features

3451d1c12e Fix docs.rs features (Alekos Filini)

Pull request description:

  ### Description

  Fix docs.rs features

  ### 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

  #### New Features:

  * [ ] I've added tests for the new feature
  * [ ] I've added docs for the new feature
  * [ ] I've updated `CHANGELOG.md`

ACKs for top commit:
  danielabrozzoni:
    utACK 3451d1c12e
  notmandatory:
    ACK 3451d1c12e

Tree-SHA512: 96dc4f816b21cf20fc2828dcfd56865f3f9add8e4aa643205879c810d09e6f2e73d6643061bf3ca98145b37e726907dedd31a145f92d6646c172a43ae2285aa8

src/wallet/mod.rs

@@ -49,6 +49,7 @@ pub(crate) mod utils;
 pub mod verify;
 
 #[cfg(feature = "hardware-signer")]
+#[cfg_attr(docsrs, doc(cfg(feature = "hardware-signer")))]
 pub mod hardwaresigner;
 
 pub use utils::IsDust;