Adding a Table of Contents in the top as well, to help guide user to
the right place.

v2:
- Use lists where necessary (Jakub)
- Language name of the code blocks must be lower-case to work with
  Gitlab properly (Jakub)
- A few missing code blocks missing (Jakub)
- Surround <> with `` to be rendered properly in Gitlab (Jakub)
- Format a few missing struct fields with `` (Jakub)
- Fix: remove wrong apostrophes when forming plural (Jakub)

Signed-off-by: Victor Toso <victortoso@redhat.com>