docs(readme): annotate skills.opper.ai link with its purpose

Adds the inline note 'fetch any skill as plain markdown' to the Skills
index link so readers know why the URL is listed.

Also serves as a re-trigger for CI now that GitHub Actions has recovered
from its degraded-service window — the prior PR (#8) merged while Actions
was down and never produced runs.

Author: Jose-Sabater

README.md

@@ -159,7 +159,7 @@ MIT
 
 ## Links
 
-- [Skills index (live)](https://skills.opper.ai)
+- [Skills index (live)](https://skills.opper.ai) — fetch any skill as plain markdown
 - [Documentation](https://docs.opper.ai)
 - [Platform](https://platform.opper.ai)
 - [Cookbook](https://github.com/opper-ai/opper-cookbook)