Document that the project is now maintained by rust-embedded/hal

Author: eldruin

README.md

@@ -2,6 +2,8 @@
 
 > Minimal and reusable non-blocking I/O layer
 
+This project is developed and maintained by the [HAL team][team].
+
 ## [Documentation](https://docs.rs/nb)
 
 ## License
@@ -19,3 +21,5 @@ at your option.
 Unless you explicitly state otherwise, any contribution intentionally submitted
 for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
 dual licensed as above, without any additional terms or conditions.
+
+[team]: https://github.com/rust-embedded/wg#the-hal-team