doc: pytest: Document the test_bind test

Add this test to the documentation. None of the functions had comments,
so attempt to explain what each does.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/pytest/test_bind.rst b/doc/develop/pytest/test_bind.rst
new file mode 100644
index 0000000..0f636a9
--- /dev/null
+++ b/doc/develop/pytest/test_bind.rst
@@ -0,0 +1,8 @@
+test_bind
+=========
+
+.. automodule:: test_bind
+   :synopsis:
+   :member-order: bysource
+   :members:
+   :undoc-members: