add instructions for local build

slides/README.md

@@ -5,3 +5,9 @@ The slides are automatically built and deployed in the CI and can be viewed at
 In order to add new slides, simply add your `.md` file in this folder, and add
 an entry to `index.md` such that your slides are linked from the landing page.
 __Important__: In `index.md`, link to your slides using `./YOUR_FILENAME.html`, and make sure to put your link at the right position in the list.
+
+To build one slide set locally, you need to have a current version of pandoc installed, see https://pandoc.org/installing.html. If your slide set is `my_slide_set.md`, you can translate it via
+```bash
+pandoc -t revealjs -s --mathjax -o test.html my_slide_set.md -V revealjs-url=https://unpkg.com/reveal.js/ -V theme=serif --include-in-header=dumux_course_header.html
+```
+and point your browser to the resulting `test.html`.