doc/upgrading: document removal of -k and -K

NEWS

@@ -7,6 +7,7 @@ Incompatible changes
   https://knot-resolver.readthedocs.io/en/v4.0.0/upgrading.html#upgrade-from-3-to-4
 - configuration: trust_anchors aliases .file, .config() and .negative were removed (!788)
 - configuration: trust_anchors.keyfile_default is no longer accessible (!788)
+- daemon: -k/--keyfile and -K/--keyfile-ro options were removed
 - meson build system is now used for builds (!771)
 - build with embedded LMBD is no longer supported
 - default modules dir location has changed

doc/upgrading.rst

@@ -15,6 +15,8 @@ Users
 
 * DNSSEC validation is now turned on by default. If you need to disable it, see
   :ref:`dnssec-config`.
+* ``-k/--keyfile`` and ``-K/--keyfile-ro`` daemon options were removed. If needed,
+  use ``trust_anchors.add_file()`` in configuration file instead.
 * In case you are using your own custom modules, move them to the new module
   location. The exact location depends on your distribution. Generally, modules previously
   in ``/usr/lib/kdns_modules`` should be moved to ``/usr/lib/knot-resolver/kres_modules``.