Rollup merge of #76534 - notriddle:doc-comments, r=jyn514

Add doc comments for From impls

#51430

Author: RalfJung

library/alloc/src/collections/binary_heap.rs

@@ -1343,6 +1343,10 @@ impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
 
 #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
 impl<T> From<BinaryHeap<T>> for Vec<T> {
+    /// Converts a `BinaryHeap<T>` into a `Vec<T>`.
+    ///
+    /// This conversion requires no data movement or allocation, and has
+    /// constant time complexity.
     fn from(heap: BinaryHeap<T>) -> Vec<T> {
         heap.data
     }

library/core/src/task/poll.rs

@@ -112,6 +112,14 @@ impl<T, E> Poll<Option<Result<T, E>>> {
 
 #[stable(feature = "futures_api", since = "1.36.0")]
 impl<T> From<T> for Poll<T> {
+    /// Convert to a `Ready` variant.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use core::task::Poll;
+    /// assert_eq!(Poll::from(true), Poll::Ready(true));
+    /// ```
     fn from(t: T) -> Poll<T> {
         Poll::Ready(t)
     }