Hello,
with dpkg -L x2gohtmlclient you can get all files provided by x2gohtmlclient on debian based systems.
in /etc/nginx/sites-available/x2gohtmlclient-demo.conf you can get simple example what do you need for working htmlclient. It contains helpfull comments for make it working.
Of cource you should have such file in /etc/nginx/sites-enabled/ Don't hesitate to ask here, if you need more information.
Best Regards, Juri Grabowski