[Observium] Adding a custom OID ?

Hello,

I'm a newbie with Observium having just installed it, but now a question has popped up in my head that I could not find a clear answer to by googling. I have a couple of Linux hosts for which I also added in the net-snmpd conf a counter for the number of imapd & others processes. How could I add to a small part of the existing graphed servers, this OID ? (or where should I look in the conf ?) I was thinking maybe defining a new template (if this is the working principle) and adding there these OIDs also for the discovery phase.

Can someone advise me at least where to start my question with ? I'm a bit confused at the moment.

Thanks, Mihai