[docs] Revise the Joy UI "Avatar" component page

[samuelsycamore]

Part of #33998

This PR revises the Joy UI "Avatar" component page.

• style and grammar changes throughout
• added info on basic/default usage and component Anatomy
• rearranged a few sections

I also added a new kind of h2 to this page, which I haven't tried elsewhere: Usage with [some other component]. I think this helps to differentiate the content from what would otherwise fall under Customization, and hopefully makes it easier for users to find. cc @oliviertassinari do you think this pattern would work in the Material UI docs as well?

https://deploy-preview-35152--material-ui.netlify.app/joy-ui/react-alert/

[mui-bot]

	Messages
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Generated by 🚫 dangerJS against 3bc85e0

[siriwatknp]

👍 Approved the Argos detection.

[danilo-leal]

Looks great!

[oliviertassinari]

I think that it would be simpler with:

Suggested change

	## Usage with the Avatar Group
	## Avatar Group

When I read "Usage with" I head with another component, but the group is part of the same component. Maybe "group" should be lowercase for the same reason.

[oliviertassinari]

I also added a new kind of h2 to this page, which I haven't tried elsewhere: Usage with [some other component]. I think this helps to differentiate the content from what would otherwise fall under Customization, and hopefully makes it easier for users to find. cc @oliviertassinari do you think this pattern would work in the Material UI docs as well?

@samuelsycamore On this page, as a user, I think that I would the first 2-3 viewports's height of the page would work better with:

1. The removal of the ## Component section. I feel that it duplicates with ## Basics. We can move the installation instructions somewhere else, but why not remove them too, there is already an overall getting started area in the section. Developers could find it.

2. The addition of a simple live demo in

so we don't have to scroll two viewports to find one. As a developer, I would personally never trust what I see in 1. because it doesn't have a preview of what it renders.

[samuelsycamore]

1. The removal of the ## Component section. I feel that it duplicates with ## Basics. We can move the installation instructions somewhere else, but why not remove them too, there is already an overall getting started area in the section. Developers could find it.

Whoops! That header is an artifact from the earlier version of the doc. I'll address that and the need for a demo under Basics in #35162. We can discuss whether or not to remove this section entirely on that PR.