Update CHANGELOG.md and document compatibility

Author: clint-white

CHANGELOG.md

@@ -6,9 +6,31 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+* `#[must_use]` attribute to many methods, porting and extending several
+  rust-lang/rust PRs
+* Method `shrink_to()` for Rust 1.56.0 and greater, ported from rust-lang/rust
+* Implementation of `From<BinaryHeap<T, C>>` for `Vec<T>` for Rust 1.41.0 or
+  greater
+* Implementation of `From<[T; N]>` for `BinaryHeap<T>` for Rust 1.56.0 or
+  greater, ported from rust-lang/rust#84111
+* Links to referenced items in the documenation
+* Example of a min-heap, ported from rust-lang/rust#60451
+* Documentation of time complexities of several methods, ported from
+  rust-lang/rust#60952
+
 ### Changed
 
 * Bump MSRV (minimum supported rust version) to rust 1.36.0.
+* Port rust-lang/rust#77435 improvement to rebuild heuristic of
+  `BinaryHeap::append()`
+* Use italics with big-O notation in documentation, ported from
+  rust-lang/rust#71167
+* Relax trait bound `C: Compare<T>` on `BinaryHeap<T, C>` struct and certain
+  methods, in part ported from rust-lang/rust#58421
+* Synchronize internal implementation details with
+  `std::collections::BinaryHeap` in Rust 1.62.0
 
 ## [0.4.1] - 2021-01-06
 

README.md

@@ -20,9 +20,15 @@ Other notable added methods are:
 - `.into_iter_sorted()` which is less-surprising version of `.into_iter()`. The implementation is backported from `std`.
 - `.replace_cmp()` which replace the comparator of the existing heap.
 
-## MSRV (Minimum Supported Rust Version)
+## Compatibility and MSRV (Minimum Supported Rust Version)
 
-This crate requires Rust 1.36.0 or later.
+This crate is based on the standard library's implementation of
+[`BinaryHeap`](https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html)
+from Rust 1.62.0.
+
+This crate requires Rust 1.36.0 or later.  A few of its APIs are only available
+for more recent versions of Rust where they have been stabilized in the
+standard library; see the documentation for specifics.
 
 # Changes