feat: add CHANGELOG to make summarizing releases easier. (#1382)

This adds a changelog in a keepachanglog.com style format.

It's initially populated with currently unreleased behavior and the last
release's (0.24.0) changes.

Work towards #1361

CHANGELOG.md

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+# rules_python Changelog
+
+This is a human-friendly changelog in a keepachangelog.com style format.
+Because this changelog is for end-user consumption of meaningful changes,only
+a summary of a release's changes is described. This means every commit is not
+necessarily mentioned, and internal refactors or code cleanups are omitted
+unless they're particularly notable.
+
+A brief description of the categories of changes:
+
+* `Changed`: Some behavior changed. If the change is expected to break a
+  public API or supported behavior, it will be marked as **BREAKING**. Note that
+  beta APIs will not have breaking API changes called out.
+* `Fixed`: A bug, or otherwise incorrect behavior, was fixed.
+* `Added`: A new feature, API, or behavior was added in a backwards compatible
+  manner.
+* Particular sub-systems are identified using parentheses, e.g. `(bzlmod)` or
+  `(docs)`.
+
+
+## Unreleased
+
+### Changed
+
+* (bzlmod) `pip.parse` can no longer automatically use the default
+  Python version; this was an unreliable and unsafe behavior. The
+  `python_version` arg must always be explicitly specified.
+
+### Fixed
+
+* (docs) Update docs to use correct bzlmod APIs and clarify how and when to use
+  various APIs.
+* (multi-version) The `main` arg is now correctly computed and usually optional.
+* (bzlmod) `pip.parse` no longer requires a call for whatever the configured
+  default Python version is.
+
+### Added
+
+* Created a changelog.
+* (gazelle) Stop generating unnecessary imports.
+* (toolchains) s390x supported for Python 3.9.17, 3.10.12, and 3.11.4.
+
+## [0.24.0] - 2023-07-11
+
+### Changed
+
+* **BREAKING** (gazelle) Gazelle 0.30.0 or higher is required
+* (bzlmod) `@python_aliases` renamed to `@python_versions
+* (bzlmod) `pip.parse` arg `name` renamed to `hub_name`
+* (bzlmod) `pip.parse` arg `incompatible_generate_aliases` removed and always
+  true.
+
+### Fixed
+
+* (bzlmod) Fixing Windows Python Interpreter symlink issues
+* (py_wheel) Allow twine tags and args
+* (toolchain, bzlmod) Restrict coverage tool visibility under bzlmod
+* (pip) Ignore temporary pyc.NNN files in wheels
+* (pip) Add format() calls to glob_exclude templates
+* plugin_output in py_proto_library rule
+
+### Added
+
+* Using Gazelle's lifecycle manager to manage external processes
+* (bzlmod) `pip.parse` can be called multiple times with different Python
+  versions
+* (bzlmod) Allow bzlmod `pip.parse` to reference the default python toolchain and interpreter
+* (bzlmod) Implementing wheel annotations via `whl_mods`
+* (gazelle) support multiple requirements files in manifest generation
+* (py_wheel) Support for specifying `Description-Content-Type` and `Summary` in METADATA
+* (py_wheel) Support for specifying `Project-URL`
+* (compile_pip_requirements) Added `generate_hashes` arg (default True) to
+  control generating hashes
+* (pip) Create all_data_requirements alias
+* Expose Python C headers through the toolchain.
+
+[0.24.0]: https://github.com/bazelbuild/rules_python/releases/tag/0.24.0
+
+