Shorten the readme

[kubaau]

The readme is very long and some of the information in it should land on GitHub pages or in a similar doc tool.

[dzeitman]

Does the Unreal Plugin Packaging supports a similar feature of optional asset and doc delivery that we use with Unity?

• We might also package and include getting started steps in a similar fashion.
• Give each version of Unreal Engine seems to be unique, perhaps each targeted SDK follows suit?
• Elsewhere, we've adopted using GitHub Pages to host SDK docs.
• Perhaps this repo has the getting started guide in a docs folder and instance and that is served up with GitHub pages?
• This slightly shifts the shared focus of presenting and maintaining SDK docs to the individual repo; with the intent that they would likely be more often updated and aligned and easy to access for the developer.

[jfan-dolby]

See branch doc-github-page for an implementation using docusaurus