Create support landing page

The creation of a "Support" landing page is overdue. It should guide the users to the several ways they can get support. Forums, handbook, howto, tutorials, books, videos, external resources, and more.

Next we can expose this Support page via the right side menu on this website, but also more pro-actively when installing MuseScore by opening the browser on this support page.

Another interesting moment to capture is when a user uninstalled MuseScore, we could push to open the browser as well to collect feedback which they uninstalled MuseScore.