doc: announce change for building deprecated libraries

As part of a larger work on selecting parts of DPDK of interests for
users, enabling deprecated libraries won't be done via the disable_libs
build option anymore.

An example of the new build option can be found at:
https://patchwork.dpdk.org/project/dpdk/patch/20230628132004.340074-2-david.marchand@redhat.com/

Signed-off-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: 0-day Robot <robot@bytheb.org>

doc/guides/rel_notes/deprecation.rst

@@ -11,6 +11,10 @@ here.
 Deprecation Notices
 -------------------
 
+* build: Enabling deprecated libraries (``flow_classify``, ``kni``) won't be
+  possible anymore through the use of the ``disable_libs`` build option. A
+  new build option for deprecated libraries will be introduced instead.
+
 * kvargs: The function ``rte_kvargs_process`` will get a new parameter
   for returning key match count. It will ease handling of no-match case.