Add a reference to the AST class reference for go

Author: owen-mc

docs/language/learn-ql/go/ql-for-go.rst

@@ -7,7 +7,10 @@ Experiment and learn how to write effective and efficient queries for CodeQL dat
    :hidden:
 
    introduce-libraries-go
+   ast-class-reference
 
 -  `Basic Go query <https://lgtm.com/help/lgtm/console/ql-go-basic-example>`__: Learn to write and run a simple CodeQL query using LGTM.
 
 -  :doc:`CodeQL library for Go <introduce-libraries-go>`: When you're analyzing a Go program, you can make use of the large collection of classes in the CodeQL library for Go.
+
+-  :doc:`Abstract syntax tree classes for Go <ast-class-reference>`: CodeQL has a large selection of classes for representing the abstract syntax tree of Go programs.