I have a raspberry pi with some ds18b20 temperature sensors attached.
I have snmpd running and during an snmpwalk (https://pastebin.com/ZNjr6At6), the custom OID’s appear (starting on line 713 of the pastebin paste) and report the temperatures.
That’s how new devices are added into LibreNMS with YAML file. Your device should now be discovered as what put into the YAML file. If you want open PR on GitHub and somebody can help you.