Documentation: Main README.md content replaced with links to wiki

[Gon-na]

This commit aims to streamline the README and wiki. For this puropse parts of the README have been replaced with links to the wiki and its chapter structure has been altered slightly.

[2xB]

Thanks for the Pull Request! While I think the deletions are great, I am not sure about the new insertions:

• The new system requirements are probably already very outdated. Also they highly depend on what you simulate, so I think especially in a README that should be short and concise, that may not be that interesting.
• Having the user guide as the first link in the README makes much sense, while the information that it uses HTML or that it is hosted by GitHub is not really interesting to the readers. So I would not move the user guide to a large section that uses such "filler information".
• Having a dependency list in the README seems like unnecessary information and duplication of what the user manual contains already.

Maybe one can replace most of the README by just a collection of links like this from a different README?

Btw. I think going from "title case" to "sentence case" (like changing the title Open Source to Open source) is a question of personal style preference.