Documentation: Kunit: Use full path to .kunitconfig

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>