Updated README to 1.2-beta3 release.
Updated README to 1.2-beta3 release.

FinnStutzenstein/OpenSlides,normanjaeckel/OpenSlides,jwinzer/OpenSlides,rolandgeider/OpenSlides,emanuelschuetze/OpenSlides,boehlke/OpenSlides,jwinzer/OpenSlides,normanjaeckel/OpenSlides,emanuelschuetze/OpenSlides,boehlke/OpenSlides,FinnStutzenstein/OpenSlides,FinnStutzenstein/OpenSlides,ostcar/OpenSlides,tsiegleauq/OpenSlides,emanuelschuetze/OpenSlides,CatoTH/OpenSlides,jwinzer/OpenSlides,CatoTH/OpenSlides,emanuelschuetze/OpenSlides,FinnStutzenstein/OpenSlides,jwinzer/OpenSlides,OpenSlides/OpenSlides,CatoTH/OpenSlides,tsiegleauq/OpenSlides,tsiegleauq/OpenSlides,ostcar/OpenSlides,jwinzer/OpenSlides,rolandgeider/OpenSlides,OpenSlides/OpenSlides,normanjaeckel/OpenSlides,boehlke/OpenSlides,boehlke/OpenSlides,ostcar/OpenSlides,normanjaeckel/OpenSlides,rolandgeider/OpenSlides,CatoTH/OpenSlides