Openrct2: Improve documentation

[Gymnasiast]

Currently, there are some problems with documentation:

1. There is not nearly enough of it.
2. User documentation and development documentation is mixed.
3. Documentation is spread out over too many places. In many cases, there is duplication, instead of linking people to the correct place. These places are:
   3.1. The OpenRCT2 wiki
   3.2. docs.openrct2.io (not working since the move from .website to .io now fixed)
   3.3. openrct2.org
   3.4. openrct2.io (Getting Started)
   3.5. readme.md

Instead, the documentation should be reorganised as follows:

1. User documentation should go to docs.openrct2.io, which should also revert to RST/ReadTheDocs.
2. Technical documentation should stay on the OpenRCT2 wiki - for now at least.
3. Both should be vastly expanded.

[Umdlye]

I just stumbled upon @telk5093's Korean documentation: https://telk.kr/orct/manual/get_start/basic_interface?v=orct&m=landscape It's gorgeous!

[Gymnasiast]

Docs repo: https://github.com/OpenRCT2/docs
Current docs: https://docs.openrct2.io/playing/footpaths.html
Archived copy of old (RTD) docs: https://web.archive.org/web/20170519180539/https://docs.openrct2.website/en/latest/playing/staff/index.html