In the beginning, I found myself quite lost as I was not totally sure how
to use Uhyve. This change introduces some additional background information
and pointers for people looking to hack on the source code.

- Make "code blocks" more consistent
- Make some wording more consistent
- Additional Markdown magic
- Cut the length of some sentences
- Add `cargo run` method for developers
- Introduce GitHub-styled admonition boxes
- Add Contributing section