Merge branch 'feature/update-readme' into 'master'

[readme] Add website's getting started guide to doc ressources

See merge request !2213

README.md

@@ -24,6 +24,7 @@ Documentation
 
 The following resources are useful to get started with DuMu<sup>x</sup>:
 
+* [Getting started guide](https://dumux.org/gettingstarted/) on the [DuMu<sup>x</sup> website](https://dumux.org/)
 * [Handbook](https://dumux.org/handbook), a detailed DuMu<sup>x</sup> manual,
 * [DuMu<sup>x</sup> course materials](https://git.iws.uni-stuttgart.de/dumux-repositories/dumux-course/tree/master),
 * [Examples](https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/tree/master/examples), with detailed description of code and results,