Bring the documentation up to date

[PaulSeitz]

• check how we can integrate the dev guides
• add sections for all the new games
• devise a method to classify our environments according to how polished they are. Would prefer something more fancy than a txt file
• update the sections about the rendering
• update installation and dependencies

[PaulSeitz]

Especially the ReadME, I think we can add a few more games (and reference the games_covered.md), update usage and note the mods and wrappers.
@sebiwtt you interested?

[sebiwtt]

Shall we have a quick call and from this I can quickly create a list of games/mods (etc.) and update the ReadME with this? @PaulSeitz