docs: comparison table of how things were done before and how they are done now

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+.. SPDX-License-Identifier: GPL-3.0-or-later
+
+With the release of version 6, there is a new way to configure and control your running ``kresd`` instances
+so that you don't have to configure multiple systemd services. The new Knot Resolver Manager handles it for you.
+In the table below, you can find comparison of how things were done before and how they can be done now.
+
+======================
+Administration changes
+======================
+
+==========================================  ===========================================================================================  ==================================================================
+Task                                        How to do it now                                                                             How it was done before           
+==========================================  ===========================================================================================  ==================================================================
+start resolver                              ``systemctl start knot-resolver``                                                            ``systemctl start kresd@1``
+stop resolver                               ``systemctl stop knot-resolver``                                                             ``systemctl stop kresd@1``
+start resolver with 4 worker processes      set ``/workers`` to 4 in the config file                                                     manually start 4 services by ``systemctl start kresd@{1,2,3,4}``
+rolling restart after updating config       ``systemctl reload knot-resolver`` (or use API or ``kresctl``)                               manually restart individual ``kresd@`` services one by one
+open logs of all instances                  ``journalctl -u knot-resolver``                                                              ``journalctl -u system-kresd.slice``
+open log of a single kresd instances        ``journalctl -u knot-resolver _PID=xxx``                                                     ``journalctl -u kresd@1``
+updating config programatically             use HTTP API or ``kresctl`` command                                                          write a custom tool to generate new config and restart ``kresd``'s
+handling errors during config changes       HTTP API just reports error, resolver keeps running with previous config                     custom tools for every user
+validate new config                         ``kresctl validate path/to/new/config.yml`` (not fully bullet proof), then try to run it     run ``kresd`` with the config and see if it fails
+look at the Lua config                      ``kresctl convert path/to/new/config.yml``                                                   ``cat /path/to/config.conf``
+gather metrics                              point Prometheus etc. at the single HTTP API                                                 collect metrics manually from all individual processes
+==========================================  ===========================================================================================  ==================================================================