CMS: change category to MinimumBias for Neutrino_Pt_2to20_gun (recid 8847)

[katilp]

Neutrino_Pt_2to20_gun http://opendata.cern.ch/record/8847 is a MinimumBias dataset.

This dataset was processed by putting together the events from the pileup MinBias dataset on top of nothing (therefore: Neutrino_Pt_2to20_gun).

Change the category from Physics Modelling to Minimum Bias and add a mention of it in the description.