You can either go to releases, and download the source as a zip or tar.gz, or you may download the entire repo as a zip, or clone it to a folder using git, your choice.
However you get the files, simply unzip (if needed), and go to File > Import > Config Bundle, and import the .ini file that is appropriate for your version of PrusaSlicer.
Then, go to Printer Settings, (change to Advanced/Expert - Simple doesn't show the needed option), and click on set bedshape, shown here.
Once opened, select the following. For Bed Texture, select CR10 Bed Texture old.png, and for Bed Mesh, Select Bed Ender3.stl.
It should look like this once finished.
My config files are far from perfect, but after searching all over, I could not find any templates to begin from, so I made my own. At the very least, it should make for a good starting place for a beginner to PrusaSlicer, or someone using the CR-20 Pro for the first time. Hopefully this helps someone else. Feel free to submit pull requests with any improvements/tweaks.