Add Superhuman Docs as external app content for FIN

We’re currently building an internal wiki/information hub in Superhuman Docs. It’s build to be a knowledge hub and team wiki, so it would be very useful to give FIN access to a specific Doc that we create for FIN. 

A useful feature in Superhuman docs is the ability to sync pages between Docs. This would allow us to sync pages from our private knowledge wiki into a wiki Doc that we give FIN access to.