docs-rst: doc-guide: split the kernel-documentation.rst contents

Having the kernel-documentation at the topmost level doesn't
allow generating a separate PDF file for it. Also, makes harder
to add extra contents. So, place it on a sub-dir.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/4.Coding.rst

@@ -358,8 +358,8 @@ them, as appropriate, for externally-available functions.  Even in areas
 which have not been so documented, there is no harm in adding kerneldoc
 comments for the future; indeed, this can be a useful activity for
 beginning kernel developers.  The format of these comments, along with some
-information on how to create kerneldoc templates can be found in the file
-Documentation/kernel-documentation.rst.
+information on how to create kerneldoc templates can be found at
+:ref:`Documentation/doc-guide/ <doc_guide>`.
 
 Anybody who reads through a significant amount of existing kernel code will
 note that, often, comments are most notable by their absence.  Once again,