[Intro page] Debunking accessibility myths

[rianrietveld]

URL: https://wpaccessibility.org/docs/start/myths/
Code: https://github.com/wpaccessibility/wp-a11y-docs/blob/main/docs/start/myths/index.md

Please read How to contribute before you start.

Task

Add short introduction text, referring to the topics mentioned in the Table of Content below the intro.