Update readme_nl.md
Update readme_nl.md

Installation instructions elaborated
devoxx4kids/materials,devoxx4kids/materials,eloudsa/materials,ooms/materials,ooms/materials,wadael/materials,devoxx4kids/materials,ooms/materials,ooms/materials,cristinanegrean/materials,henkjurriens/materials,eloudsa/materials,wadael/materials,eloudsa/materials,devoxx4kids/materials,devoxx4kids/materials,cristinanegrean/materials,cristinanegrean/materials,DevCamp4Kids/materials,ooms/materials,henkjurriens/materials,ooms/materials,vorburger/materials,DevCamp4Kids/materials,vorburger/materials,ooms/materials,devoxx4kids/materials,DevCamp4Kids/materials,wadael/materials,DevCamp4Kids/materials,henkjurriens/materials,wadael/materials,devoxx4kids/materials,henkjurriens/materials,cristinanegrean/materials,vorburger/materials,vorburger/materials