Add accessibility-ready testing docs

[joedolson]

Adds initial structure for the accessibility-ready guidelines. DRAFT only.

Please note:
Content committed without contacting the project leads @rianrietveld or @joedolson first, will not be reviewed.

The related issue number: #

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• One of the project leads assigned this task to you.
• You did not generate content using AI (artificial intelligence), except for translations or spelling checks.

If you submit code or documentation using a local build:

• Your code builds clean without any errors or warnings while running npm run test.
• You read the documentation in How to contribute to this documentation.
• You checked the modified pages with an accessibility tool like Axe Devtools or WAVE.

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2025-12-23 06:33 UTC

[joedolson]

Changes requested below!

[amberhinds]

This PR closes: #164

It adds two new sections under Standards and best practice:

• Documenting Accessibility
• Theme accessibility guidelines

And one new section under Testing WordPress themes:

• Testing WordPress themes for accessibility