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/SecurityBugs b/Documentation/SecurityBugs
index 10a1f79..342d769 100644
--- a/Documentation/SecurityBugs
+++ b/Documentation/SecurityBugs
@@ -1,3 +1,5 @@
+.. _securitybugs:
+
 Security bugs
 =============