Documentation/HOWTO: add cross-references to other documents

Add cross references for the documents mentioned at HOWTO and
are under the Documentation/ directory, using the ReST notation.

It should be noticed that HOWTO also mentions the /README file.
We opted to not touch it, for now, as making it build on
Sphinx would require it to be moved to a Documentation/foo
directory.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/stable_api_nonsense.txt b/Documentation/stable_api_nonsense.txt
index 9187b4e..24f5aee 100644
--- a/Documentation/stable_api_nonsense.txt
+++ b/Documentation/stable_api_nonsense.txt
@@ -1,3 +1,5 @@
+.. _stable_api_nonsense:
+
 The Linux Kernel Driver Interface
 ==================================