Added the description for transparent_layer_bar.json.
Added the description for transparent_layer_bar.json.

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