[FR] Own properties for IOCs

[Athryss]

First off all - great project!

Is your feature request related to a problem? Please describe.
I would like to add my own property to IOCs. I would like to add IOC properties like "Description", "TLP", "Flow", etc. myself. For example - Timestamp (To track when it was first found)

Describe the solution you'd like
Please describe in the documentation how to add your own to property to IOCs.