docs: document autosizing behavior (#7097)
docs: document autosizing behavior (#7097)

#7096
uwdata/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite