Update quick start docs to discuss distribution

[stackotter]

The quick start docs should be self-contained and should answer all beginner Swift Bundler questions in addition to SwiftCrossUI questions. Therefore we should have a section that discusses app distribution and the various bundlers available in today's Swift Bundler. That section should also mention how to make a release build, and the intricacies of distributing a WinUIBackend app at the moment (needs users to manually install the windows app runtime I believe). If it makes sense, we could put platform-specific distribution intricacies in the backend pages and then link off to those sections for problematic backends.

We should also make it clear that swift bundler vs swift-bundler is due to a SwiftPM feature that only works on some platforms.

Thanks to Maxim in the Discord server for reporting these shortcomings!