[Docs] Add announcement about 2.0 and our paper to the index page
[Docs] Add announcement about 2.0 and our paper to the index page

Fix #1501

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