Automatically generate setup HTML from Markdown

[davidschreiber]

The setup screen shows a simple HTML file setup-guide.html stored in the app's assets: https://github.com/PSPDFKit-labs/QuickDemo/blob/master/app/src/main/assets/setup-guide.html

This file is generated from a Markdown template: https://github.com/PSPDFKit-labs/QuickDemo/blob/master/setup-guide.md

Right now this has to be done manually, and is thus prone to mistakes. A PR fixing this issue should add automated Markdown-to-HTML conversion to the app's build script, so that the file is properly regenerated on every build.