Added the bytemuck optional dependency to lib.rs documentation

This is so that it is easier to find and more consistent with the
other optional dependencies

src/lib.rs

@@ -108,6 +108,7 @@
 //! * `fast-rng` - uses a faster algorithm for generating random UUIDs.
 //!   This feature requires more dependencies to compile, but is just as suitable for
 //!   UUIDs as the default algorithm.
+//! * `bytemuck` - adds a `Pod` trait implementation to `Uuid` for byte manipulation
 //!
 //! # Unstable features
 //!