Create an accessibility landing / routing page at jupyter.org/accessibility

Right now, Jupyter doesn't have a single obvious landing page to help people understand where they can learn more about accessibility. That said, there are a lot of different user interfaces in Jupyter and its subprojects, and also different definitions of "accessibility". People have a hard time navigating all of these spaces, and are often unsure what is authoritative, what is up to date, etc.

I suggest that we create a single "landing page" that helps point people in the right direction, at an authoritative and easy to remember URL.

### To do / questions

- [ ] Is this overall idea reasonable? Any objections?
- [ ] Any changes you'd make to the structure below?

### Suggestion: jupyter.org/accessiblity

This would be a landing page to frame the general goals for accessibility across Jupyter, and provide links to places where readers can learn more. It probably wouldn't be an evergreen page with constantly updated content, but would instead link to other evergreen places that we expect to be more up to date. For example:

```
[Statement of accessibility goals across Jupyter].
[Honest take on where we are right now (e.g., we've made progress, and still have plenty of improvements to make, something like that)]

## Accessibility subproject provides cross-project guidance and strategy

[A few bullets about the purpose of this group and its role in jupyter, a link to learn more].

[link to the accessibility subproject docs (is that still the readthedocs site?)]

## Where to engage around accessibility

[Links to the meetings or spaces where accessibility is discussed]
[E.g., a github issue tag, zulip channel, calendar meeting, etc]

## Project-specific accessibility documentation

[A statement about how subprojects manage their own accessibility work]
[A list of links to each one that Chris knows of, e.g.:

- jupyter book's accessibility page (https://mystmd.org/guide/accessibility-and-performance)
- similar pages for jupyter hub or lab
```

### What this would *not* be

- A place with full information about accessibility, tools, practices, etc. IMO that's the accessibility subproject docs.
- A place with up to date information about the state of accessibility of each subproject (instead, it'd link to _their_ accessibility statements)

### References and lnks

- Jupyter Book accessibility page (and see linked myst page in it): https://jupyterbook.org/accessibility/