[Sane] Wiki updates

[O. A. Rondon]

I've updated the BigCal section of the wiki with two entries, one with
slides describing the detector and its dimensions, the other describing
the calibration method with pi0 mass reconstruction used by Hovhannes.

https://hallcweb.jlab.org/experiments/sane/wiki/index.php/BigCal

These updates are to address questions by Jixie and Whit at yesterday's
analysis meeting.

Cheers,

Oscar