docs: submit-checklist: Allow creating cross-references for ABI README

Now that Documentation/ABI is processed by automarkup, let it
generate cross-references for the ABI README file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/76e60ee8717551f3d15d7c92b9c93bbf2ca8cff3.1739254867.git.mchehab+huawei@kernel.org

Author: mchehab

Documentation/process/submit-checklist.rst

@@ -52,7 +52,7 @@ Provide documentation
 4) All new module parameters are documented with ``MODULE_PARM_DESC()``
 
 5) All new userspace interfaces are documented in ``Documentation/ABI/``.
-   See ``Documentation/ABI/README`` for more information.
+   See Documentation/ABI/README for more information.
    Patches that change userspace interfaces should be CCed to
    linux-api@vger.kernel.org.