doc: Move Kconfig next to build system section
doc: Move Kconfig next to build system section

yogo1212/RIOT,basilfx/RIOT,miri64/RIOT,authmillenon/RIOT,miri64/RIOT,kYc0o/RIOT,OlegHahm/RIOT,yogo1212/RIOT,kaspar030/RIOT,yogo1212/RIOT,smlng/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,authmillenon/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,smlng/RIOT,authmillenon/RIOT,smlng/RIOT,smlng/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,smlng/RIOT,jasonatran/RIOT,ant9000/RIOT,OlegHahm/RIOT,miri64/RIOT,yogo1212/RIOT,OTAkeys/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,basilfx/RIOT,yogo1212/RIOT,authmillenon/RIOT,kYc0o/RIOT,OTAkeys/RIOT,basilfx/RIOT,authmillenon/RIOT,ant9000/RIOT,miri64/RIOT,jasonatran/RIOT,basilfx/RIOT,kaspar030/RIOT,basilfx/RIOT,ant9000/RIOT,kYc0o/RIOT,OlegHahm/RIOT,miri64/RIOT,authmillenon/RIOT,RIOT-OS/RIOT