docs: add info to open payments catchup call (#276)

README.md

@@ -29,3 +29,15 @@ The code for the landing [page](https://openpayments.guide) is in `./landing`.
 
 - [Payment Pointers](https://paymentpointers.org)
 - [Interledger](https://interledger.org)
+
+## Open Payments Catchup Call
+
+Our catchup calls are open to our community. We have them every Monday at 11:00 GMT, via Google Meet.
+
+Video call link: https://meet.google.com/htd-eefo-ovn
+
+Or dial: (DE) +49 30 300195061 and enter this PIN: 105 520 503#
+
+More phone numbers: https://tel.meet/htd-eefo-ovn?hs=5
+
+[Add to Google Calendar](https://calendar.google.com/calendar/event?action=TEMPLATE&tmeid=MTdkZTEwYThhNjliNDUxOGJmNTc0ZWE2NjgxZWViZjlfMjAyMzA4MjhUMTEwMDAwWiBzYWJpbmVAaW50ZXJsZWRnZXIub3Jn&tmsrc=sabine%40interledger.org&scp=ALL)