Update google-drive-picker.mdx (#320)

Co-authored-by: Merlijn Vos <[email protected]>

Author: mifi

docs/sources/companion-plugins/google-drive-picker.mdx

@@ -71,6 +71,11 @@ yarn add @uppy/google-drive-picker
 
 Using Google Drive Picker requires setup in both Uppy and Companion.
 
+### Prerequisites
+
+Make sure your web app is hosted on a server that either does **not set
+`Cross-Origin-Opener-Policy` at all** or sets it to `same-origin-allow-popups`.
+
 ### Initial setup
 
 To sign up for API keys, go to the