chore: Improve UX for global config

[clabby]

Overview

The first thing st asks you to do is set up your global config with a github PAT. It's easy to skip over this on accident.

We should add a st config command to edit this config, and a warning log if the github_token is not set inside of the global configuration to reduce confusion.

[blmalone]

yea, my natural reaction was to hit enter instead of e to edit the config file so I skipped this step entirely.

[blmalone]

first pass at implementing this here: #29