Add some guidance on how to develop the accessibility model of a new control

[scottaohara]

This would be a follow on to https://github.com/openui/open-ui/pull/469 and would involve resolving the TODO within the get involved page.

The TODO presently states:

Add some guidance on how to develop the accessibility model of a new control based on prior art in ARIA. Also add information on where to raise issues, e.g: authoring practices task force - raise an issue - tagged in x way.

[github-actions[bot]]

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.

[scottaohara]

going to assign myself to my own issue. i'll try to work on this soon (this may not be actually what happens, but i'll try)