Reference zipimport source code from docs. (GH-13310)

diff --git a/Doc/library/zipimport.rst b/Doc/library/zipimport.rst
index aa1831d..2138697 100644
--- a/Doc/library/zipimport.rst
+++ b/Doc/library/zipimport.rst
@@ -6,6 +6,8 @@
 
 .. moduleauthor:: Just van Rossum <just@letterror.com>
 
+**Source code:** :source:`Lib/zipimport.py`
+
 --------------
 
 This module adds the ability to import Python modules (:file:`\*.py`,