Howto include RRDGraph PHP class in linuxserver/nginx?


I’m using RRD to make some data from weather sensors visible.
I thought, that it’s time to move my code to a Docker instance and linuxserver/ningx sounds interesting.

But I’d like to ask how to integrate the “rrd_graph” tool into this instance?
I see this error in the logs:
FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Class ‘RRDGraph’ not found

I found this guide (RRD Graph | NGINX), but I really appreciate your support if you can guide me to integrate this into the docker instance.

Best Regards,