Adding custom help in the Help menu would require customization as out of the box, custom help can be added on:

• Entity profiles:
 •  at the top of the profile (entity level)
 •  on each section of the profile
 • Dialog boxes and inline views for creating/editing entities (edit screens):
 •  at the top of the edit screen (entity level)
 •  on each dialog box tab or inline view section

Alternatively we can suggest creating a new section item instead, which points to your help page.