Fix broken URL in README.md

Author: 9names

embedded-hal-bus/README.md

@@ -38,7 +38,7 @@ provides mechanisms to obtain multiple `I2c` instances out of a single `I2c` ins
   `portable-atomic` emulates atomic CAS functionality, allowing `embedded-hal-bus` to use `atomic-device` on hardware
   that does not natively support atomic CAS. If you enable this, you must also add `portable-atomic` to your crate with
   a feature flag such as `unsafe-assume-single-core` or `critical-section` to choose how atomic CAS is implemented.
-  See https://docs.rs/portable-atomic/1.7.0/portable_atomic/#optional-features for more info.
+  See <https://docs.rs/portable-atomic/1.7.0/portable_atomic/#optional-features> for more info.
 - **`std`**: enable shared bus implementations using `std::sync::Mutex`, and implement
   `std::error::Error` for `DeviceError`.