KUnit: Docs: make start.rst example Kconfig follow style.rst

The primary change is that we want to encourage people to respect
KUNIT_ALL_TESTS to make it easy to run all the relevant tests for a
given config.
Signed-off-by: NDaniel Latypov <dlatypov@google.com>
Reviewed-by: NBrendan Higgins <brendanhiggins@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kunit/start.rst

@@ -196,8 +196,9 @@ Now add the following to ``drivers/misc/Kconfig``:
 .. code-block:: kconfig
 
 	config MISC_EXAMPLE_TEST
-		bool "Test for my example"
+		tristate "Test for my example" if !KUNIT_ALL_TESTS
 		depends on MISC_EXAMPLE && KUNIT=y
+		default KUNIT_ALL_TESTS
 
 and the following to ``drivers/misc/Makefile``: