State that resolve() does nothing outside of continue_on (#717)

* State that resolve() does nothing outside of continue_on

* throw

* errorcode

Author: cbiesinger

spec/index.bs

@@ -1732,6 +1732,11 @@ their phone number. To allow for such flows, the [=IDP=] must call
 
 See the [=show an IDP login dialog=] algorithm for more details.
 
+{{IdentityProvider/resolve}} is used while a [=show a continuation
+dialog|continuation dialog=] is shown to return a specific token to the [=RP=]
+as described below. If called at any other time, reject the returned
+promise with a "{{NotAllowedError}}" {{DOMException}}.
+
 An {{IdentityUserInfo}} represents user account information from a user. This information is exposed
 to the [=IDP=] once the user has already used the FedCM API to login in the [=RP=]. That is, it is
 exposed when there exists an account |account| such that the [=connected accounts set=] [=list/contains=]