docs: Document virtualenv for docs project

[xmudrii]

Summary

The Development Environment document for the Documentation project suggests running pip to install the needed dependencies. However, starting with Python 3.11, it's not possible to run plain pip install because it fails with the following error:

error: externally-managed-environment

with the recommendation to use virtualenv or pipx. See this StackOverflow answer for more details about this change.

To conform to this requirement, the Development Environment document has been extended to cover creating and activating virtualenv.

Location

https://docs.flybywiresim.com/dev-corner/development-projects/documentation-project/documentation/#required-tools

Discord username (if different from GitHub): xmudrii

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 4, 2024 6:54pm

[Valastiri]

only one thing and this will be good to merge.

There's some other changes i'd like on this page but of scope for PR can be done later.

[Valastiri]

Suggested change

	```
	!!! info "Using `virtualenv`"
	Starting with Python 3.11, the `pip` tool will fail to install dependencies and packages globally, instead it's recommended to use `virtualenv`. If you desire to install packages globally, you must use another tool, such as [`pipx`](https://github.com/pypa/pipx). We recommend using `virtualenv` because it's easier and the recommended way to work on Python projects.
	!!! danger "Activating `virtualenv`"
	It's important to note that `virtualenv` activation is not persisted. If you restart your terminal/command prompt and want to work on the documentation project again, you have to reactivate your `virutalenv` using the appropriate activation command that was shown earlier in this guide.
	- Install dependencies with this single line command:
	```title="Run In Terminal"
	pip install -r requirements.txt
	```
	```
	- Install dependencies with this single line command:
	```title="Run In Terminal"
	pip install -r requirements.txt
	```
	!!! info "Using `virtualenv`"
	Starting with Python 3.11, the `pip` tool will fail to install dependencies and packages globally, instead it's recommended to use `virtualenv`. If you desire to install packages globally, you must use another tool, such as [`pipx`](https://github.com/pypa/pipx). We recommend using `virtualenv` because it's easier and the recommended way to work on Python projects.
	!!! danger "Activating `virtualenv`"
	It's important to note that `virtualenv` activation is not persisted. If you restart your terminal/command prompt and want to preview your work on the documentation project again, you have to reactivate your `virutalenv` using the appropriate activation command that was shown earlier in this guide.

Ideally i'd like to move this step below the rest of the instructions and have the admonitions follow as "extra information" so the flow is neater when "reading".

Additionally, in the second admonition "Activiation virtual env" just a small change as spinning up the server isn't technically required when working on docs.

[xmudrii]

@Valastiri pushed a commit to fix this. Just to confirm, should Create and activate a Python Virtual Environment stay as it is right now?