App-ads.txt mail from AdMob

So I just received email from AdMob about something called App-ads.txt.

Without any knowledge about this, this is completely unknown to me. So my question is: What is it? Is there something we should do? Will this change something? Performance wise.

The email was received today, and today is 08.08.2019, the date this enforcement starts. So what’s happening?whatsapp web whatsapp plus