Improved PinnedDrop docs

Author: y86-dev

rust/kernel/init.rs

@@ -643,7 +643,29 @@ where
 
 /// Trait facilitating pinned destruction.
 ///
-/// Use [`pinned_drop`] to implement this trait safely.
+/// Use [`pinned_drop`] to implement this trait safely:
+/// ```rust
+/// # use kernel::sync::Mutex;
+/// use kernel::macros::pinned_drop;
+/// #[pin_project]
+/// struct Foo {
+///     #[pin]
+///     mtx: Mutex<usize>,
+/// }
+///
+/// #[pinned_drop]
+/// impl PinnedDrop for Foo {
+///     fn drop(self: Pin<&mut Self>) {
+///         pr_info!("Foo is being dropped!");
+///     }
+/// }
+/// ```
+///
+/// # Safety
+///
+/// This trait must be implemented with [`pinned_drop`].
+///
+/// [`pinned_drop`]: kernel::macros::pinned_drop
 pub unsafe trait PinnedDrop {
     /// # Safety
     ///