core, doc, cli (forums): new forums set commands + doc:

- document the fact that if an empty `uri` is used, the forum node is created
  automatically
- new `forums/set` CLI commands and its documentation

doc/libervia-cli/forums.rst

@@ -28,6 +28,22 @@ Get structure of French forums in JSON::
 
   $ li forums get -k fr -O json
 
+set
+===
+
+Set forums from JSON, the JSON must be given as input.
+
+Check :ref:`libervia-cli_blog_edit` for the data format.
+
+example
+-------
+
+Set the forums structure from a ``forums.json`` file::
+
+  $ li forums set < forums.json
+
+
+.. _libervia-cli_forums_edit:
 
 edit
 ====
@@ -51,6 +67,8 @@ metadata are set. You can use the following metadata:
 ``uri``
   URI to the PubSub node containing the messages of the topic (it's actually a blog node
   with suitable permissions). URI must only be set for topic, not for categories.
+  If ``uri`` is empty, a node will be created automatically and the ``uri`` will be filled
+  accordingly.
 ``sub-forums``
   list of object with the same metadata (i.e. other topics or categories)