2015: add link to slides and notes for adonovan's GothamGo talk

whose title is "Using go/types for Code Comprehension and Refactoring Tools".

Change-Id: Id0bf5a5f9908c43c6cd738add2ee7dd58f164358
Reviewed-on: https://go-review.googlesource.com/15390
Reviewed-by: Andrew Gerrand <adg@golang.org>