Add a privacy policy

[brianhelba]

Explain what information we collect on users and how it's stored.

The site does not service "any individual who seeks or
acquires, by purchase or lease, any goods, services, money, or credit
for personal, family, or household purposes", so we're not yet required to post a policy by California law, but it's a decent guide for what to include: http://leginfo.ca.gov/cgi-bin/displaycode?section=bpc&group=22001-23000&file=22575-22579