some accessibility statements in other (potential) recs

At the core meeting, I was tasked to look at some spec for how they handle
the accessibility requirements.

There is some semi-boilerplate that seems to be in line with our thoughts
for "simple" in response to the APA requests (see below for examples). They
are in the spec itself, not an appendix. However, they tend to be towards
the end near sections on security, privacy, and internationalization.

To me, it seems fine to add another appendix near the current ones entitled
"Accessibility Considerations".

Some examples:
https://www.w3.org/TR/vc-bitstring-status-list/#accessibility-considerations
https://www.w3.org/TR/vc-jose-cose/#accessibility
https://www.w3.org/TR/vc-data-model-2.0/#accessibility-considerations
https://www.w3.org/TR/epub-33/#sec-accessibility