Add documentation about our data/Matomo policy

[NeuroShepherd]

Can be added to either our About page or a separate privacy page. About is probably best IMO

[NeuroShepherd]

1. Our whole database should have cookies disabled by default
2. When generating the tracking code for individual sites, we disable the cookie tracking
3. IP addresses are anonymized to the /16 subnet level i.e. 255.255.XXX.XXX which is approximately state/region level
4. Data only used for internal tracking purposes for mainly 1) knowing what sites are being used frequently and in particular the pages people use and 2) demonstrating value for grants. Only OSC members have access to the data, and, at that, it is aggregated data.

[NeuroShepherd]

lmu-osc/manual#21