This feature is no yet part of the new add-on. There are two workarounds:
Go to “Cog menu > Manage references” and add the references from there. It’s just one click.
Add the citations via the “P” button in the Google Docs toolbar or “Paperpile > Insert citation” menu. This will automatically import all references you cite from a web search to your library (we probably will make this the default behavior of our new sidebar add-on as well)