doc: Start improving our pytest documentation

Begin the work of documenting all of our pytests. To do this, we should
have a directory under develop for it as there will be a large number of
new files. As the current document is referenced externally in a number
of locations, add the sphinx_reredirects module so that we can redirect
from the old location to the new.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/tests_writing.rst b/doc/develop/tests_writing.rst
index f6f852c..0621946 100644
--- a/doc/develop/tests_writing.rst
+++ b/doc/develop/tests_writing.rst
@@ -376,5 +376,5 @@
 Writing Python tests
 --------------------
 
-See :doc:`py_testing` for brief notes how to write Python tests. You
+See :doc:`pytest/usage` for brief notes how to write Python tests. You
 should be able to use the existing tests in test/py/tests as examples.