Bump minimum Rust version to 1.24

README.md

@@ -122,6 +122,8 @@ Hyperfine can be installed via [cargo](https://doc.rust-lang.org/cargo/):
 cargo install hyperfine
 ```
 
+Make sure that you use Rust 1.24 or higher.
+
 ### From binaries (Linux, macOS)
 
 Download the corresponding archive from the [Release page](https://github.com/sharkdp/hyperfine/releases).