external_monitoring callback hook is not documented

[etnt]

Hi,

I don't think this 'external_monitoring' callback hook is documented, or? Should probably be documented in the system_monitor.app.src file.

https://github.com/klarna/system_monitor/blob/1978c2b165514a7be4108f5778a92abf0eff5bc4/src/system_monitor_events.erl#L68

Cheers, Tobbe

[mikpe]

PRs welcome. We're unfortunately short on bandwidth for GH right now.

[etnt]

Ok, will do.