docs(pipstar): add more docs to make it ready for release (#3323)

Followup to #3225 to add more documentation.

Author: aignas

CHANGELOG.md

@@ -81,7 +81,8 @@ END_UNRELEASED_TEMPLATE
   With this release we are deprecating {obj}`pip.parse.experimental_target_platforms` and
   {obj}`pip_repository.experimental_target_platforms`. For users using `WORKSPACE` and
   vendoring the `requirements.bzl` file, please re-vendor so that downstream is unaffected
-  when the APIs get removed.
+  when the APIs get removed. If you need to customize the way the dependencies get
+  evaluated, see [our docs](/pypi/download.html#customizing-requires-dist-resolution) on customizing `Requires-Dist` resolution.
 
 {#v0-0-0-fixed}
 ### Fixed

docs/environment-variables.md

@@ -71,6 +71,9 @@ instead of the legacy Python scripts.
 
 :::{versionadded} 1.5.0
 :::
+:::{versionchanged} VERSION_NEXT_FEATURE
+Flipped to be enabled by default.
+:::
 ::::
 
 ::::{envvar} RULES_PYTHON_EXTRACT_ROOT

docs/pypi/download.md

@@ -168,11 +168,6 @@ available on the PyPI index that you use.
 
 ### Customizing `Requires-Dist` resolution
 
-:::{note}
-Currently this is disabled by default, but you can turn it on using 
-{envvar}`RULES_PYTHON_ENABLE_PIPSTAR` environment variable.
-:::
-
 In order to understand what dependencies to pull for a particular package,
 `rules_python` parses the `whl` file [`METADATA`][metadata].
 Packages can express dependencies via `Requires-Dist`, and they can add conditions using