boards/iotlab-m3: Fix units & alignment in doc
boards/iotlab-m3: Fix units & alignment in doc

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