docs: minor updates to pyenv installs (#4189)

Contributing.md

@@ -23,10 +23,6 @@ To work and develop PyO3, you need Python & Rust installed on your system.
 * [virtualenv](https://virtualenv.pypa.io/en/latest/) can also be used with or without Pyenv to use specific installed Python versions.
 * [`nox`][nox] is used to automate many of our CI tasks.
 
-### Caveats
-
-* When using pyenv on macOS, installing a Python version using `--enable-shared` is required to make it work. i.e `env PYTHON_CONFIGURE_OPTS="--enable-shared" pyenv install 3.7.12`
-
 ### Help users identify bugs
 
 The [PyO3 Discord server](https://discord.gg/33kcChzH7f) is very active with users who are new to PyO3, and often completely new to Rust. Helping them debug is a great way to get experience with the PyO3 codebase.

guide/src/getting-started.md

@@ -18,19 +18,14 @@ To use PyO3, you need at least Python 3.7. While you can simply use the default
 
 While you can use any virtualenv manager you like, we recommend the use of `pyenv` in particular if you want to develop or test for multiple different Python versions, so that is what the examples in this book will use. The installation instructions for `pyenv` can be found [here](https://github.com/pyenv/pyenv#getting-pyenv). (Note: To get the `pyenv activate` and `pyenv virtualenv` commands, you will also need to install the [`pyenv-virtualenv`](https://github.com/pyenv/pyenv-virtualenv) plugin. The [pyenv installer](https://github.com/pyenv/pyenv-installer#installation--update--uninstallation) will install both together.)
 
-If you intend to run Python from Rust (for example in unit tests) you should set the following environment variable when installing a new Python version using `pyenv`:
-```bash
-PYTHON_CONFIGURE_OPTS="--enable-shared"
-```
+It can be useful to keep the sources used when installing using `pyenv` so that future debugging can see the original source files. This can be done by passing the `--keep` flag as part of the `pyenv install` command.
 
 For example:
 
 ```bash
-env PYTHON_CONFIGURE_OPTS="--enable-shared" pyenv install 3.12
+pyenv install 3.12 --keep
 ```
 
-You can read more about `pyenv`'s configuration options [here](https://github.com/pyenv/pyenv/blob/master/plugins/python-build/README.md#building-with---enable-shared).
-
 ### Building
 
 There are a number of build and Python package management systems such as [`setuptools-rust`](https://github.com/PyO3/setuptools-rust) or [manually](./building-and-distribution.md#manual-builds). We recommend the use of `maturin`, which you can install [here](https://maturin.rs/installation.html). It is developed to work with PyO3 and provides the most "batteries included" experience, especially if you are aiming to publish to PyPI. `maturin` is just a Python package, so you can add it in the same way you already install Python packages.