This PR adds a reading guide to the home page and to a separate page within Start with accessibility.

Previews: home: https://wpaccessibility.org/pr-preview/pr-283
Start with accessibility: https://wpaccessibility.org/pr-preview/pr-283/docs/start/guide/

Content is taken from the research by @AnneliesDT
props: @AnneliesDT

The related issue number: #59

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

Before submitting this PR, please make sure:

• 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.