[README] link slide pages

README.md

@@ -5,7 +5,7 @@
 The material is organized as follows
 
 * __Exercises__: click [here](./exercises/README.md) to go to the exercise description
-* __Slides__: click [here](./slides/README.md) to download the slides
+* __Slides__: click [here](https://pages.iws.uni-stuttgart.de/dumux-repositories/dumux-course/index#/title-slide) to view the slides
 * __Links__: click [here](./links/README.md) to go to a list of useful links
 
 ## Installation of the course