Update User-Guide.md
Update User-Guide.md

we are on python3. Update the documentation.
certtools/intelmq,certtools/intelmq,pkug/intelmq,aaronkaplan/intelmq,pkug/intelmq,certtools/intelmq,pkug/intelmq,aaronkaplan/intelmq,pkug/intelmq,aaronkaplan/intelmq