[docs] add a note about the external translation dependency to translation docs
[docs] add a note about the external translation dependency to translation docs

RayRutjes/Silex,akucherevskiy/developex_test,mmauri04/Silex,cesarmarinhorj/Silex,SpacePossum/Silex,naderman/Silex,stof/Silex,lokhman/Silex,mathroc/Silex,GromNaN/Silex,peterkokot/Silex,mTorres/Silex,GromNaN/Silex,stof/Silex,SpacePossum/Silex,CarsonF/Silex,romainneutron/Silex,jdreesen/Silex,mTorres/Silex,Tobion/Silex,Xephi/Silex,mathroc/Silex,romainneutron/Silex,mmauri04/Silex,peterkokot/Silex,silexphp/Silex,gencer/Silex,lyrixx/Silex,Incognito/silex-fork,cgsmith/Silex,beealone/Silex,Tobion/Silex,SanderKnape/Silex,fhinkel/Silex,fhinkel/Silex,naderman/Silex,Incognito/silex-fork,peterkokot/Silex,cesarmarinhorj/Silex,lokhman/Silex,plotek/Silex,Xephi/Silex,akucherevskiy/developex_test,arduanov/Silex,GromNaN/Silex,lyrixx/Silex,naderman/Silex,fabpot/Silex,CarsonF/Silex,JPry/Silex,cgsmith/Silex,tcx1000/Silex,Seldaek/Silex,Seldaek/Silex,RayRutjes/Silex,plotek/Silex,arduanov/Silex,stof/Silex,Tobion/Silex,fabpot/Silex,SanderKnape/Silex,romainneutron/Silex,lyrixx/Silex,akucherevskiy/developex_test,JPry/Silex,tcx1000/Silex,jdreesen/Silex,beealone/Silex,CarsonF/Silex