Umbrella issue: ensure documentation is accessible

**This is a Feature Request**

**What would you like to be added**
Look at the set of documentation (initially, the English localization).
Review this against [ARIA](https://www.w3.org/TR/wai-aria/) (Accessible Rich Internet Applications) guidelines / specifications.
Make changes to ensure that the documentation is accessible.

**Why is this needed**
> Education and collaboration are vital to the future of the CNCF ecosystem and it is imperative to us that everyone in the community that wants to participate feels welcome to do so regardless of gender, gender identity, sexual orientation, disability, race, ethnicity, age, religion or economic status.

— CNCF

**Comments**
Treat this as an overarching / epic issue.
After identifying room for improvement, log a specific issue about making that improvement, and mention this issue in the description of the new issue.

Review the English documentation against the WAI-ARIA guidelines and specifications, starting with the documentation set rather than a named file or entry point. Record each accessibility improvement as a separate issue, linking it back to this umbrella issue; done means the identified documentation improvements have been scoped into specific follow-up work.

Written by the indexing model from the issue text.