Merge pull request #2087 from aviramha/contributing_improvements

Add setting up a dev environment notes

Author: davidhewitt

Contributing.md

@@ -15,6 +15,17 @@ You can browse the API of the non-public parts of PyO3 [here](https://pyo3.rs/in
 
 The following sections also contain specific ideas on where to start contributing to PyO3.
 
+## Setting up a development environment
+
+To work and develop PyO3, you need Python & Rust installed on your system.
+* We encourage the use of [rustup](https://rustup.rs/) to be able to select and choose specific toolchains based on the project.
+* [Pyenv](https://github.com/pyenv/pyenv) is also highly recommended for being able to choose a specific Python version.
+* [virtualenv](https://virtualenv.pypa.io/en/latest/) can also be used with or without Pyenv to use specific installed Python versions.
+
+### 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 Gitter channel](https://gitter.im/PyO3/Lobby) 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.