Remove an unused use declaration in the docs (#8)

It appears `PathBuf` is unused here since the example now shows `u32`.

README.md

@@ -83,7 +83,6 @@ input=testing
 ## Compatible Types
 [`FileOrStdin`] can wrap any type that matches the trait bounds for `Arg`: `FromStr` and `Clone`
 ```rust
-use std::path::PathBuf;
 use clap::Parser;
 use clap_stdin::FileOrStdin;