v0.0.4 - Description

Add logo, remove domain-specific "therapist" from the quickstart example

Logo embedded via an absolute raw.githubusercontent.com URL in the
README, since both GitHub's repo "description" field (plain text only,
can't hold images) and PyPI's rendered page (which reads this README,
not GitHub's description) need an absolute URL to resolve an image -
relative paths don't reliably work on PyPI's renderer.

Swapped the quickstart's "therapist" example value for something domain-
neutral ("admin"), since pgfire isn't tied to any one application's
vocabulary.