Update FEC.gov content guide for accessibility

[jason-upchurch]

Summary

What we're after:
We would like to ensure the content guide conforms to style, e.g., accessibility

Suggested completion criteria

• review content guide content for conformance to rules specified in content guide
• have team discussion to consider publishing the content guide in one of our repository wiki's for version control and transparency

[JonellaCulmer]

This is done, so closing.

[jason-upchurch]

added "have team discussion" to completion criteria.
issue reopened ensure team inputs. No milestone assigned so that this issue doesn't get in the way of other work this sprint.

[dorothyyeager]

Content team has decided to close this issue in favor of a more general review to follow the work we've done migrating court cases and Audit reports. New issue is at #4335