Update CivicActions Handbook

[mgifford]

CA's single source of truth has been the handbook. Clearly this is a useful resource which needs to be maintained and whose content must be closely linked with this site to avoid duplication/confusion.

https://handbook.civicactions.com/en/latest/060-engineering/accessibility/

• [ ] Add bookmark links

[jerseycheese]

TODO:

• [x] Audit for old/outdated info
• [x] Audit for highly specific guidance that could be prone to becoming dated
• [x] Followup for writing up additional/new info
• [x] https://github.com/CivicActions/accessibility/issues/35#issuecomment-769987795

[mgifford]

These Handbook PR's need to be socialized with the project leads before getting approved.

• Adding information about accessibility in social media
• Adding paragraph about accessibility for wireframes

[jerseycheese]

gDoc being used for auditing CA Handbook pages that contain a11y info: https://docs.google.com/document/d/1k1vk80LQwzgMZKXn1cln451s830Z8q7ruPjzt7mpEIM/edit#

[jerseycheese]

@mgifford or @lukefretwell Can you review my suggestions/comments to existing CA handbook a11y info/pages here? https://docs.google.com/document/d/1k1vk80LQwzgMZKXn1cln451s830Z8q7ruPjzt7mpEIM/edit#

Afterwards, I will submit a PR for the handbook.

Thanks!

[lukefretwell]

@mgifford I default to you on this. cc @jerseycheese

[lukefretwell]

From #101:

The main site and handbook are linked from the handbook here:

https://handbook.civicactions.com/en/latest/050-how-we-work/bookmarks/#useful-accessibility-extensions-to-install

I'd like folks at CA to be reminded about the accessibility site here and for them to bookmark it.