rust: types: add examples for the Either type

We aim to have examples in all Rust types, thus add basic ones for the
`Either` type.

Suggested-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Nell Shamrell-Harrington <nells@linux.microsoft.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://rust-for-linux.zulipchat.com/#narrow/stream/291565/topic/x/near/467478085
Link: https://lore.kernel.org/r/20240918212052.8790-1-nells@linux.microsoft.com
[ Reworded slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: Nell Shamrell-Harrington

rust/kernel/types.rs

@@ -461,6 +461,15 @@ impl<T: AlwaysRefCounted> Drop for ARef<T> {
 }
 
 /// A sum type that always holds either a value of type `L` or `R`.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::types::Either;
+///
+/// let left_value: Either<i32, &str> = Either::Left(7);
+/// let right_value: Either<i32, &str> = Either::Right("right value");
+/// ```
 pub enum Either<L, R> {
     /// Constructs an instance of [`Either`] containing a value of type `L`.
     Left(L),