DOC: add link for Mock library

Author: matthew-brett

doc/source/links_names.txt

@@ -82,6 +82,7 @@
 .. _emacs_python_mode: http://www.emacswiki.org/cgi-bin/wiki/PythonMode
 .. _doctest-mode: http://ed.loper.org/projects/doctestmode/
 .. _nose: http://somethingaboutorange.com/mrl/projects/nose
+.. _mock: https://github.com/testing-cabal/mock
 .. _`python coverage tester`: http://nedbatchelder.com/code/coverage/
 .. _bitbucket: https://bitbucket.org