docs: Append to /etc/modules, not overwrite
docs: Append to /etc/modules, not overwrite

Fixes the snd_bcm2835 module not being loaded and therefore sound output not working
priestd09/mopidy,pacificIT/mopidy,ZenithDK/mopidy,quartz55/mopidy,jodal/mopidy,dbrgn/mopidy,vrs01/mopidy,diandiankan/mopidy,bencevans/mopidy,mopidy/mopidy,woutervanwijk/mopidy,woutervanwijk/mopidy,ZenithDK/mopidy,jmarsik/mopidy,bacontext/mopidy,quartz55/mopidy,jodal/mopidy,jcass77/mopidy,liamw9534/mopidy,dbrgn/mopidy,jmarsik/mopidy,mokieyue/mopidy,hkariti/mopidy,jodal/mopidy,hkariti/mopidy,diandiankan/mopidy,SuperStarPL/mopidy,ali/mopidy,swak/mopidy,diandiankan/mopidy,SuperStarPL/mopidy,mopidy/mopidy,bacontext/mopidy,swak/mopidy,pacificIT/mopidy,abarisain/mopidy,mopidy/mopidy,kingosticks/mopidy,dbrgn/mopidy,jmarsik/mopidy,quartz55/mopidy,mokieyue/mopidy,bencevans/mopidy,kingosticks/mopidy,ali/mopidy,vrs01/mopidy,mokieyue/mopidy,diandiankan/mopidy,abarisain/mopidy,adamcik/mopidy,ali/mopidy,hkariti/mopidy,tkem/mopidy,jmarsik/mopidy,vrs01/mopidy,glogiotatidis/mopidy,jcass77/mopidy,liamw9534/mopidy,quartz55/mopidy,rawdlite/mopidy,ali/mopidy,bencevans/mopidy,ZenithDK/mopidy,adamcik/mopidy,pacificIT/mopidy,swak/mopidy,SuperStarPL/mopidy,rawdlite/mopidy,tkem/mopidy,rawdlite/mopidy,bacontext/mopidy,tkem/mopidy,pacificIT/mopidy,jcass77/mopidy,ZenithDK/mopidy,glogiotatidis/mopidy,swak/mopidy,mokieyue/mopidy,glogiotatidis/mopidy,dbrgn/mopidy,vrs01/mopidy,kingosticks/mopidy,SuperStarPL/mopidy,bencevans/mopidy,tkem/mopidy,rawdlite/mopidy,adamcik/mopidy,bacontext/mopidy,priestd09/mopidy,priestd09/mopidy,hkariti/mopidy,glogiotatidis/mopidy