Feature request: Add Drupal VPAT to site and explain how it is different

[mgifford]

Is your feature request related to a problem? Please describe. Highlight https://github.com/CivicActions/accessibility/tree/main/VPAT work and encourage folks to submit pull requests. Highlight how we used this basic VPAT to MD file.

Describe the solution you'd like A page possibly in the Guide. Although, we probably need a whole Drupal section.