Offer alternative Linux builds on Download page

[almereyda]

Describe the idea

Link to the current AppImage on https://www.digital-democracy.org/mapeo/download/ in so non-developer users of non-Debian-based systems can quickly start into Mapeo.

What's your role? Where and how do you currently use the application?

Not all users of alternative distributions like me can find the developer link and will pursue additional search engine requests to find an answer to their question how to install Mapeo Desktop.

What is your ideal step by step workflow?

1. Go to the Download page.
2. Reject the automatic .deb download
3. Find a link to the AppImage at the bottom of the page

Have you thought about what it might look like?

The alternative download link could be hidden behind a little drop-down arrow on the Linux button.

If Linux is detected from userAgent, as currently, only those identifying as Debian-based distributions could be offered the .deb, and others would be offered a suitable alternative.

Additional context

If these can be achieved fairly easy on the Electron platform, an rpm or FlatPak build appears feasible, too. And if one's at it, and to finish the cycle, widening the build spectrum to Snaps closes the gap that AppImages initially also intend to address.