Account Linking: add note about paid feature
Account Linking: add note about paid feature

https://trello.com/c/Ls4VJv0J/1002-linking-user-accounts

hamzawi06/docs,yvonnewilson/docs,auth0/docs,jeffreylees/docs,hamzawi06/docs,hamzawi06/docs,khorne3/docs,sandrinodimattia/docs,auth0/docs,khorne3/docs,yvonnewilson/docs,auth0/docs,khorne3/docs,yvonnewilson/docs,sandrinodimattia/docs,sandrinodimattia/docs,jeffreylees/docs,jeffreylees/docs