Adding examples from The Carpentries on Accessibility of our Lessons

### How could the content be improved?

In the [section teaching on Accessibility](https://carpentries.github.io/instructor-training/09-eia.html#accessibility), could we consider adding examples of how The Carpentries has designed its lessons and lesson infrastructure to be accessible? We could consider listing what are some of the features the community created/modified to address accessibility concerns, features that Instructors can be made aware of and apply in teaching or bring to the attention of their leaners. The section feels a bit abstract, yet we have many practical examples we could incorporate to illustrate the principles of universal design and accessibility support also incorporated in our systems.

@sstevens2 please add any thoughts you may have here on this too.

### Which part of the content does your suggestion apply to?

https://carpentries.github.io/instructor-training/09-eia.html#accessibility

Start by reading the Accessibility section in 09-eia.html#accessibility and review the lesson and lesson-infrastructure examples available in the project. Identify concrete Carpentries accessibility features that instructors can explain or apply, then add them to make the universal-design discussion more practical.

Written by the indexing model from the issue text.