fix: Additional dependencies for development #6085

[alexvoss]

I added instructions for working on Insiders and also changed the instructions for installing optional dependencies to use the definitions in pyproject.toml.

As I keep forgetting to activate a venv and end up installing things globally, I added a note about getting pip to refuse installing things outside a venv. Seems I am not the only person who keeps making that mistake, so I thought it would be useful for people here as many of our customers will not be hard-core Pythonistas.

Hope this fits the bill. I got stuck on this a little bit because I looked for ways to make things run on Windows but that is a battle we can fight another day, perhaps when we find someone who is native in that environment.

[squidfunk]

Great work! Only some minor changes.

[squidfunk]

I meant to put that into a code annotation, similar to the section below. Sorry if this was unclear. It's definitely valuable information and we should mention it, but I'd regard it as side content to the interested reader:
https://squidfunk.github.io/mkdocs-material/getting-started/#with-pip-9x

[alexvoss]

Ah, sorry, you mean like so?

=== "Insiders"
    
    You will need to have a GitHub access token [as described in the
    Insiders documentation] and make it available in the `$GH_TOKEN`
    variable. 
  
    ``` sh
    git clone https://${GH_TOKEN}@github.com/squidfunk/mkdocs-material-insiders.git # (1)!
    ```

    1. If you are using SSH keys for authenticating with GitHub, you can
       clone Insiders with this command:
       ```
       git clone git@github.com:squidfunk/mkdocs-material-insiders.git
       ``` 
       
    [as described in the Insiders documentation]: insiders/getting-started.md#requirements

I had to remove the line before the code snippet in the annotation to force it to be rendered inside the annotation and not as a next line. The documentation for the code annotation feature does not say anything about the rules for defining the annotation? Is this down to indentation? (may need to better learn Markdown's rules on that)

[alexvoss]

I've gone and pushed this version, hope it fits the bill.

[squidfunk]

I had to remove the line before the code snippet in the annotation to force it to be rendered inside the annotation and not as a next line. The documentation for the code annotation feature does not say anything about the rules for defining the annotation?

I think this happens because you need to indent by four spaces, not three, like so:

mkdocs-material/docs/getting-started.md

Lines 33 to 55 in 5ba7944

	=== "9.x"
	``` sh
	pip install mkdocs-material=="9.*" # (1)!
	```
	1. Material for MkDocs uses [semantic versioning][^2], which is why it's a
	good idea to limit upgrades to the current major version.
	This will make sure that you don't accidentally [upgrade to the next
	major version], which may include breaking changes that silently corrupt
	your site. Additionally, you can use `pip freeze` to create a lockfile,
	so builds are reproducible at all times:
	```
	pip freeze > requirements.txt
	```
	Now, the lockfile can be used for installation:
	```
	pip install -r requirements.txt
	```

[alexvoss]

yep, that fixed it. It might be an idea to create an example for this that points these subtleties out? (I will try to push a branch with some examples tomorrow, I hope)

[squidfunk]

Thanks! LGTM!