Documentation: Kunit: Add ref for other kinds of tests

Add an organic link to the "other kinds of tests" in the index page

Signed-off-by: Tales Aparecida <[e-mail]>
Reviewed-by: David Gow <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

Documentation/dev-tools/kunit/faq.rst

···
 
 For more information, see :ref:`kunit-on-non-uml`.
 
+.. _kinds-of-tests:
+
 What is the difference between a unit test and other kinds of tests?
 ====================================================================
 Most existing tests for the Linux kernel would be categorized as an integration

Documentation/dev-tools/kunit/index.rst

···
 - Improves code quality.
 - Encourages writing testable code.
 
+Read also :ref:`kinds-of-tests`.
+
 How do I use it?
 ================