Facebook is adding a new shopping section to its main app, part of a broader push to capitalise on the increase in online retail in the midst of the Covid-19 outbreak.The new section, Facebook Shop, was to start rolling out across the US on Tuesday. It lets people browse product catalogues from businesses and buy items on the social network.Facebook was previously testing the section with a small group of US users, and launched a similar feature on its Instagram photo-sharing app last month…