Docs: Explicitly state that AiiDA's Group API and CLI can be used

It is not directly obvious to users that AiiDA's group APIs can be used
with pseudopotential families since they are simply groups themselves.

docs/source/design.rst

@@ -53,6 +53,12 @@ Families
 ========
 
 Having loose pseudopotentials floating around is not very practical, so groups of related pseudopotentials can be organized into "families", which are implemented as group plugins with the base class :py:class:`~aiida_pseudo.groups.family.PseudoPotentialFamily`.
+
+.. tip::
+
+    Since a :py:class:`~aiida_pseudo.groups.family.PseudoPotentialFamily` is a subclass of AiiDA's :py:class:`~aiida.orm.groups.Group`, they share the same API.
+    That means you can use `AiiDA's group API <https://aiida.readthedocs.io/projects/aiida-core/en/latest/howto/data.html#organizing-data>`_ as well as the ``verdi group`` CLI to work with families of ``aiida-pseudo``.
+
 A family class can in principle support many pseudopotential formats, however, a family instance can only contain pseudopotentials of a single format.
 For example, the :py:class:`~aiida_pseudo.groups.family.PseudoPotentialFamily` class supports all of the pseudopotential formats that are supported by this plugin.
 However, any instance can only contain pseudopotentials of the same format (e.g. *all* UPF or *all* PSP8, not a mixture).