This is an example gallery description. You can list images explicitly (as above,
with per-image alt, optional nsfw, optional width/height for external
images, and an optional feature flag for the mosaic layout) or use
galleryFolder: my-folder to pull every image under galleries/my-folder/ from
the image manifest.
Set layout: in the frontmatter to choose the arrangement: justified (default,
tiled mosaic), grid, masonry, or mosaic.