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/index.rst b/doc/develop/index.rst
index c907f8c..0c83ef1 100644
--- a/doc/develop/index.rst
+++ b/doc/develop/index.rst
@@ -82,7 +82,7 @@
    :maxdepth: 1
 
    testing
-   py_testing
+   pytest/index
    tests_writing
    tests_sandbox
    binman_tests