Documentation
README
What would the skill do? One or two sentences. What does the freelancer paste in, what do they get back?
When would someone reach for it? The moment in the Upwork workflow it serves.
What would it be built from? Upwork's published guidance, your own field experience, or both. No invented stats, sources get cited.
Are you offering to write it? Yes / no is fine either way. Proposals without an author still help the roadmap.