readme: add tested up to 3.7.1
readme: add tested up to 3.7.1

katrinleinweber/podlove-publisher,noplanman/podlove-publisher,katrinleinweber/podlove-publisher,podlove/podlove-publisher,noplanman/podlove-publisher,katrinleinweber/podlove-publisher,podlove/podlove-publisher,noplanman/podlove-publisher,noplanman/podlove-publisher,katrinleinweber/podlove-publisher,katrinleinweber/podlove-publisher,podlove/podlove-publisher,noplanman/podlove-publisher,podlove/podlove-publisher,podlove/podlove-publisher,podlove/podlove-publisher