docs: fix "example gallery" link in layering docs
docs: fix "example gallery" link in layering docs

Signed-off-by: Stephan Renatus <3d1a7d0a294b6d8e799ad6e122143905f17f9530@chef.io>

vega/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite