Update docs to reflect `config use_venv` deprecation

[dexterlemmer]

Is your feature request related to a problem? Please describe.

I noticed that at https://pdm.fming.dev/2.1/usage/advanced/ the Use Nox as the runner section contains the following sentence:

"Before running nox, you should also pdm config use_venv true to enable venv reusing."

However, in bash I get the following:

$ pdm config use_venv
DEPRECATED: the config has been renamed to python.use_venv
True
$ pdm config python.use_venv
True

Describe the solution you'd like

Update the above mentioned sentence under Use Nox as the runner as follows:

- "Before running nox, you should also pdm config use_venv true to enable venv reusing."
+"Before running nox, you should also pdm config python.use_venv true to enable venv reusing."

I would be willing to make a PR if you ask me. But I may not be able to get around to it for a while.

---

Edit: I didn't check if the docs are outdated anywhere else.

[frostming]

+"Before running nox, you should also pdm config python.use_venv true to enable venv reusing."

This sentence can be removed as the venv has been enabled by default. Welcome to PR.

[dexterlemmer]

+"Before running nox, you should also pdm config python.use_venv true to enable venv reusing."

This sentence can be removed as the venv has been enabled by default. Welcome to PR.

OK. I'll make a PR to remove the sentence sometime this weekend.

[dexterlemmer]

Thinking about this. We can certainly remove the sentence. But may be we should still keep something like it but qualified to only be necessary if you're using PEP582.