Quick Help now goes to Video Tutorials (which don't exist yet).

Also emphasise 'Audacity Manual' in the help menu.

With this change I'm being careful to make sure it's clear that the manual is for Audacity rather than for DarkAudacity.  For the time being DarkAudacity is for people who know Audacity already and want to try the dark theme.  Because of that, it is enough to highlight the differences between Audacity and DarkAudacity and link to the existing Audacity manual.  If the differences continue to grow over time wit future editions, then I will need the promised 'Video Tutorials'.  So I link to the page for them now.  That page will have their up to date status information.