pre-commit install instructions are incomplete

[encukou]

The current pre-commit install instructions are listed before the “Compile and build” section:

$ pre-commit install --allow-missing-config
pre-commit installed at .git/hooks/pre-commit

This doesn't work before pre-commit itself is installed, and it can't be installed if one doesn't have Python yet.

[hugovk]

The instructions in full are:

---

Install pre-commit as a Git hook

To make sure your code is linted correctly, we recommend setting up pre-commit as a Git hook:

$ pre-commit install --allow-missing-config
pre-commit installed at .git/hooks/pre-commit

Now pre-commit will run automatically on git commit.

---

That pre-commit link is to https://pre-commit.com/#installation which shows a couple of ways to install pre-commit.

I don't think we need to instruct people how to install Python itself: I think if someone wants to contribute to Python development, they will already have a Python installation, or know how to do so. And if nothing else, the front page of the devguide begins with instructions on how to build Python.