Documentation: Kunit: Use full path to .kunitconfig

The numbered list contains full path to every files that need to be
modified or created in order to implement misc-example kunit test.
Except for .kunitconfig. Which might make a newcommer confused about
where the file exists. Since there are multiple .kunitconfig files.

Fix this by using the full path to .kunitconfig.

Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kunit/start.rst

@@ -265,7 +265,7 @@ Now we are ready to write the test cases.
 
 	obj-$(CONFIG_MISC_EXAMPLE_TEST) += example_test.o
 
-4. Add the following lines to ``.kunitconfig``:
+4. Add the following lines to ``.kunit/.kunitconfig``:
 
 .. code-block:: none