docs: update skill publishing for committed-skills workflow

[carsonfarmer]

Summary

Update the publishing instructions to reflect the simplified skills management approach.

New Workflow

Skills are committed files, not bootstrapped dependencies:

# Clone repo - skills come with it
git clone git@github.com:recallnet/skunkworks-template.git

# Update skills via gh CLI
gh skill update --all
git add .agents/skills/
git commit -m "chore: update skills"

See skunkworks-template PR #21.