Add a description of H1 Marketing

[RobTobias123]

Outcome

A description of how and when (guidance) to apply the id="marketing" - added to the Docs Typography page. It has became apparent that some people didn't know it existed unless they were to read the code in the live example. With description it will help inform.

Scope

Draft a sentence and suggest placement within the appropriate page.
Check with team and community this satisfies the need.