docs: add ArtifactHub listing for Helm chart

[pmady]

Summary

Add an artifacthub-repo.yml to the repo root so the Helm chart is discoverable on ArtifactHub.

What to do

1. Create artifacthub-repo.yml at repo root with the repo ID and owner info
2. Register the repository on artifacthub.io
3. Verify the chart shows up after the next scan

Example

repositoryID: <generated-uuid>
owners:
  - name: pmady
    email: <maintainer-email>

Reference

See keda-gpu-scaler's artifacthub-repo.yml.

Acceptance criteria

• artifacthub-repo.yml committed
• Chart listed on artifacthub.io
• ArtifactHub badge added to README

Difficulty: Beginner — config file + web registration