doc (cli/pubsub): document new --public flags:

`--public` option is documented for `subscribe`, `subscriptions` and `node subscriptions
get`, with examples. A warning has been added to show explicitely the privacy implication
of using `--public` with `subscribe`.

rel 365

doc/libervia-cli/pubsub_node_subscriptions.rst

@@ -13,6 +13,13 @@ get
 
 Retrieve subscriptions to a node.
 
+If ``--public`` is used, only public subscriptions are retrieved (if target service
+supports `XEP-0465 Public Pubsub Subscriptions`). Public subscriptions are accessible to
+anybody, thus you can use this on a node even if you are not an owner of it (and thus
+would not normally be allowed to retrieve subscriptions).
+
+.. _XEP-0465 Public Pubsub Subscriptions: https://xmpp.org/extensions/inbox/pubsub-public-subscriptions.html
+
 example
 -------
 
@@ -20,6 +27,10 @@ Get subscription from ``some_node``::
 
   $ li pubsub node subscriptions get -n some_node
 
+Retrieve public subscribers to the blog of Louise::
+
+  $ li pubsub node subscriptions get --public -s louise@example.org -n urn:xmpp:microblog:0
+
 set
 ===