Add missing permissions (#372)

docs/sandbox-permissions-reference.rst

@@ -10,6 +10,7 @@ complete list can be viewed using ``flatpak build-finish --help``.
 
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 ``--socket=x11``                                     Show windows using X11
+``--socket=fallback-x11``                            Grant X11 access when Wayland is not available
 ``--share=ipc``                                      Share IPC namespace with the host [#f1]_
 ``--allow=bluetooth``                                Allow access to Bluetooth
 ``--device=dri``                                     OpenGL rendering
@@ -18,6 +19,11 @@ complete list can be viewed using ``flatpak build-finish --help``.
 ``--share=network``                                  Access the network [#f2]_
 ``--talk-name=org.freedesktop.secrets``              Talk to a named service on the session bus
 ``--system-talk-name=org.freedesktop.GeoClue2``      Talk to a named service on the system bus
+``--socket=cups``                                    Talk to the CUPS printing system
+``--socket=gpg-agent``                               Talk to the GPG agent
+``--socket=pcsc``                                    Grant access to smart card
+``--socket=ssh-auth``                                SSH authentication
+``--socket=session-bus``                             Unlimited access to user's D-Bus session
 ``--socket=system-bus``                              Unlimited access to all of D-Bus
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