docs: document usb-logger and usb-dfu

embassy-usb-logger/README.md

@@ -13,3 +13,17 @@ async fn logger_task(driver: Driver<'static, USB>) {
     embassy_usb_logger::run!(1024, log::LevelFilter::Info, driver);
 }
 ```
+
+## Minimum supported Rust version (MSRV)
+
+Embassy is guaranteed to compile on the latest stable Rust version at the time of release. It might compile with older versions but that may change in any new patch release.
+
+## License
+
+This work is licensed under either of
+
+- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
+  <http://www.apache.org/licenses/LICENSE-2.0>)
+- MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
+
+at your option.