docs(toh6): fix if-docs (#3116)
docs(toh6): fix if-docs (#3116)

Fix: we can’t have a markdown `<span>` ranging over multiple
paragraphs; instead we use the `+ifDocsFor()` mixin.
realappie/angular.io,realappie/angular.io,realappie/angular.io,realappie/angular.io,realappie/angular.io