user/faq: add entry about using Jami in a LAN or offline

Change-Id: I8ee95608d1b31f6ee713e83005c60c1d9ac52e77

user/faq.rst

@@ -627,6 +627,28 @@ If you run your own TURN server:
 
 -  TURN/STUN: TCP+UDP 3478, 5349
 
+Can I use Jami in a local network (LAN) without internet access?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Yes!  Thanks to Jami's architecture, Jami users on a local/private
+network can communicate among themselves using Jami, without requiring
+any outside connectivity such as the internet.
+
+To do so, from Jami's ``Account`` settings open ``Advanced account
+settings``.  There, enable the ``Enable local peer discovery``
+setting.  Additionally, you may want to manually set the ``bootstrap``
+node's address (default: ``bootstrap.jami.net``) to the IP address of
+another device on your network that also runs Jami and/or an OpenDHT
+node.
+
+.. note:: If you will use this Jami account for communicating only
+   with only with other devices on the same local/private network,
+   you can disable TURN if you wish.  If you do so, and later you
+   decide to use this account also for communicating with other Jami
+   devices outside your network, don't forget to enable TURN again,
+   as it helps Jami work around issues with some overly restrictive
+   firewalls.
+
 How can I configure the codecs even more?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~