v 1.0 doc punchlist

[pq]

docs for 1.0:

• [ ] README
• [ ] API docs
  • [ ] levels in general
  • [ ] how to log an error in particular https://github.com/pq/logs/issues/12#issuecomment-431887937

[pq]

Regrading levels, @devoncarew adds:

Ah, to follow up on my review, somewhere in the API - where int level is defined - we should have some indication of what the appropriate values are. Perhaps just a pointer to the package:logging docs, and something like an example that an 'error' level maps to a value of 1000.

👍