Add CHANGELOG entry and update conversions guide

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Implement type information for conversion failures. [#1050](https://github.com/PyO3/pyo3/pull/1050)
 - Add `PyBytes::new_with` and `PyByteArray::new_with` for initialising Python-allocated bytes and bytearrays using a closure. [#1074](https://github.com/PyO3/pyo3/pull/1074)
 - Add `Py::as_ref` and `Py::into_ref`. [#1098](https://github.com/PyO3/pyo3/pull/1098)
+- Add optional implementations of `ToPyObject`, `IntoPy`, and `FromPyObject` for [hashbrown](https://crates.io/crates/hashbrown)'s `HashMap` and `HashSet` types. The `hashbrown` feature must be enabled for these implementations to be built. [#1114](https://github.com/PyO3/pyo3/pull/1114/)
 
 ### Changed
 - Exception types have been renamed from e.g. `RuntimeError` to `PyRuntimeError`, and are now only accessible by `&T` or `Py<T>` similar to other Python-native types. The old names continue to exist but are deprecated. [#1024](https://github.com/PyO3/pyo3/pull/1024)

guide/src/conversions.md

@@ -24,10 +24,10 @@ The table below contains the Python type and the corresponding function argument
 | `float`       | `f32`, `f64`                    | `&PyFloat`           |
 | `complex`     | `num_complex::Complex`[^1]      | `&PyComplex`         |
 | `list[T]`     | `Vec<T>`                        | `&PyList`            |
-| `dict[K, V]`  | `HashMap<K, V>`, `BTreeMap<K, V>` | `&PyDict`          |
+| `dict[K, V]`  | `HashMap<K, V>`, `BTreeMap<K, V>`, `hashbrown::HashMap<K, V>`[^2] | `&PyDict` |
 | `tuple[T, U]` | `(T, U)`, `Vec<T>`              | `&PyTuple`           |
-| `set[T]`      | `HashSet<T>`, `BTreeSet<T>`     | `&PySet`             |
-| `frozenset[T]` | `HashSet<T>`, `BTreeSet<T>`    | `&PyFrozenSet`       |
+| `set[T]`      | `HashSet<T>`, `BTreeSet<T>`, `hashbrown::HashSet<T>`[^2] | `&PySet` |
+| `frozenset[T]` | `HashSet<T>`, `BTreeSet<T>`, `hashbrown::HashSet<T>`[^2] | `&PyFrozenSet` |
 | `bytearray`   | `Vec<u8>`                       | `&PyByteArray`       |
 | `slice`       | -                               | `&PySlice`           |
 | `type`        | -                               | `&PyType`            |
@@ -250,3 +250,4 @@ fn main() {
 [`PyRefMut`]: https://docs.rs/pyo3/latest/pyo3/pycell/struct.PyRefMut.html
 
 [^1]: Requires the `num-complex` optional feature.
+[^2]: Requires the `hashbrown` optional feature.