[TASK] Updated README / INSTALL / NEWS files

* Added README.md (which was formerly part of the individual
  distributions)
* Transformed the text into markdown for nice visualisation i.e.
  on Github
* Rewritten the installation steps
* Rewritten the system requirements

Releases: 6.2
Resolves: #53745
Change-Id: I293bde1a046e9f7c712d5d8d9cc13138a303efc2
Reviewed-on: https://review.typo3.org/25490
Reviewed-by: Michael Stucki
Tested-by: Michael Stucki
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny