docs: Ask readers to install swh.model[cli] to fully use swh-identify

Otherwise, they will get an error asking them to install Click
(or Dulwich if Click installed and they use -t snapshot)

docs/persistent-identifiers.rst

@@ -300,7 +300,7 @@ third party.  An implementation of SWHID that allows to do so locally is the
 `swh identify <https://docs.softwareheritage.org/devel/swh-model/cli.html>`_
 tool, available from the `swh.model <https://pypi.org/project/swh.model/>`_
 Python package under the GPL license. This package can be installed via the ``pip``
-package manager with the one liner ``pip3 install swh.model`` on any machine with
+package manager with the one liner ``pip3 install swh.model[cli]`` on any machine with
 Python  (at least version 3.7) and ``pip`` installed (on a Debian or Ubuntu system a simple ``apt install python3 python3-pip``
 will suffice, see `the general instructions <https://packaging.python.org/tutorials/installing-packages/>`_ for other platforms).