ed448/README.md: add Rust logo to crates.io badge

Author: tarcieri

ed448/README.md

@@ -48,7 +48,7 @@ dual licensed as above, without any additional terms or conditions.
 
 [//]: # (badges)
 
-[crate-image]: https://img.shields.io/crates/v/ed448
+[crate-image]: https://img.shields.io/crates/v/ed448?logo=rust
 [crate-link]: https://crates.io/crates/ed448
 [docs-image]: https://docs.rs/ed448/badge.svg
 [docs-link]: https://docs.rs/ed448/