Update verify-access-token.md
Update verify-access-token.md

Added note about Custom Domains and Token Issuance (mostly copied over from the Custom Domains page)
yvonnewilson/docs,auth0/docs,jeffreylees/docs,yvonnewilson/docs,yvonnewilson/docs,auth0/docs,auth0/docs,jeffreylees/docs,jeffreylees/docs