docs: Add upmpdcli as an alternative to Rygel
docs: Add upmpdcli as an alternative to Rygel

Based on PR #871 by @woutervanwijk.

Fixes #871

mopidy/mopidy,SuperStarPL/mopidy,rawdlite/mopidy,bencevans/mopidy,dbrgn/mopidy,kingosticks/mopidy,dbrgn/mopidy,diandiankan/mopidy,quartz55/mopidy,priestd09/mopidy,tkem/mopidy,diandiankan/mopidy,kingosticks/mopidy,vrs01/mopidy,glogiotatidis/mopidy,quartz55/mopidy,vrs01/mopidy,jcass77/mopidy,ZenithDK/mopidy,mokieyue/mopidy,glogiotatidis/mopidy,bencevans/mopidy,glogiotatidis/mopidy,mokieyue/mopidy,rawdlite/mopidy,bacontext/mopidy,pacificIT/mopidy,adamcik/mopidy,jcass77/mopidy,adamcik/mopidy,SuperStarPL/mopidy,ali/mopidy,pacificIT/mopidy,jodal/mopidy,hkariti/mopidy,adamcik/mopidy,tkem/mopidy,bacontext/mopidy,ali/mopidy,priestd09/mopidy,mokieyue/mopidy,ZenithDK/mopidy,ZenithDK/mopidy,tkem/mopidy,vrs01/mopidy,rawdlite/mopidy,dbrgn/mopidy,bacontext/mopidy,ali/mopidy,jmarsik/mopidy,diandiankan/mopidy,mokieyue/mopidy,hkariti/mopidy,rawdlite/mopidy,ZenithDK/mopidy,jodal/mopidy,bencevans/mopidy,jcass77/mopidy,SuperStarPL/mopidy,mopidy/mopidy,quartz55/mopidy,dbrgn/mopidy,jodal/mopidy,glogiotatidis/mopidy,SuperStarPL/mopidy,jmarsik/mopidy,ali/mopidy,hkariti/mopidy,swak/mopidy,bencevans/mopidy,pacificIT/mopidy,hkariti/mopidy,mopidy/mopidy,tkem/mopidy,swak/mopidy,pacificIT/mopidy,jmarsik/mopidy,priestd09/mopidy,swak/mopidy,quartz55/mopidy,vrs01/mopidy,jmarsik/mopidy,diandiankan/mopidy,swak/mopidy,kingosticks/mopidy,bacontext/mopidy