✨ [hub/collections] document the image gallery/viewer (#1032)
* ✨ [hub/collections] document the image gallery/viewer
* Update docs/hub/collections.md
* ✨ Add dark mode images
* ⏪ Revert "✨ Add dark mode images"
This reverts commit b437f64da3737cc0c04bf4ba5db2de43ded04cfa.
