Minor update re: np.arccos

[patrickmineault]

Requested in an email from one of the content creators:

I see you also logged another minor change to the code:

Moved from arccos of cos metric to straight cosine matrix (there was no explanation and it was confusing)

The change is from np.arccos(rdms_comp) to 1 - rdms_comp

I discussed this with Niko (cc'd) today. Both of these are distance measures, but the difference is that arccos gives us an angle and makes the whole rdm comparison a metric. That's why we had it there. I think it would be good to go back to that.

Niko and Heiko have a slide in their deck (see below) that explains what a metric is so we can actually add more explanation on that if you think that would help.

[glibesyck]

Added in #383.