Documentation for usage without events dataset out of date

[firste]

Problem Summary

With the UX improvements in 0.2.0 release, configuration expectations for events became more strict and the events section in usage config is required. We previously had documentation about how to configure seismometer without an event file in the FAQ that needs to be amended.

Suggested fix

Readd the following to the FAQ RST
'''
events:
- source: Target Column Name
display_name: Target Column Display Name
usage: target
'''