Add accessibility docs for title and description elements

[lindseywild]

Is your feature request related to a problem? Please describe.
The work that is being done in #2732 would be great to add to the docs about how to use the title and description elements to create more accessible charts.

Describe the solution you'd like
Documentation explaining the updates, why they're important, and how to use them.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
This is dependent on #2732 and which chart types have implemented the new fields. I think it should wait until that issue is complete before doing this.

[knsv]

There are some info about this in the docs:
https://mermaid-js.github.io/mermaid/#/accessibility?id=defining-accessibility-options

Can we close this issue?

[lindseywild]

@knsv Yep - thank you! If there are follow up suggestions I can open a new story 😄