docs: deprecate kernel-doc-nano-HOWTO.txt

Now that the new Sphinx world order is taking over, the information in
kernel-doc-nano-HOWTO.txt is outmoded.  I hate to remove it altogether,
since it's one of those files that people expect to find.  But we can add a
warning and fix all the other pointers to it.

Reminded-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index cd077ca..cb9a6c6 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -255,10 +255,10 @@
 	- directory with info about the kernel build process.
 kdump/
 	- directory with mini HowTo on getting the crash dump code to work.
-kernel-doc-nano-HOWTO.txt
-	- mini HowTo on generation and location of kernel documentation files.
 kernel-docs.txt
 	- listing of various WWW + books that document kernel internals.
+kernel-documentation.rst
+	- how to write and format reStructuredText kernel documentation
 kernel-parameters.txt
 	- summary listing of command line / boot prompt args for the kernel.
 kernel-per-CPU-kthreads.txt