doc: underline links
The current use of color only to differentiate links fails WCAG A accessibility standards.
Possible solutions are:
- Using a text indicator to show that the text is a link.
- Using additional cues (such as underlining).
- Providing color contrast of 3:1 or greater with surrounding text (not the background--the adjacent text!) along with visual cues on hover.
The solution here implements the second option.
Ref: https://www.w3.org/WAI/WCAG21/Understanding/use-of-color.html Ref: https://www.w3.org/WAI/WCAG21/Techniques/failures/F73 Ref: https://www.w3.org/WAI/WCAG21/Techniques/general/G182