Update sightings for MISP IOCs detected

[arvchristos]

MISP provides an API to add or remove sightings for each attribute. Should we detect a match, we can increase the sightings number, helping to curate more valuable events by providing direct feedback.

Relevant PyMISP method: https://pymisp.readthedocs.io/en/latest/modules.html#pymisp.PyMISP.add_sighting