Document the fact that these devices are allocated at runtime using

cloning and point to two common methods of doing so.

share/man/man4/faith.4

@@ -45,6 +45,18 @@ for implementing userland IPv6-to-IPv4 TCP relay
 like
 .Xr faithd 8 .
 .Pp
+Each
+.Nm
+interface is created at runtime using interface cloning.
+This is
+most easily done with the
+.Xr ifconfig 8
+.Cm create
+command or using the
+.Va cloned_interfaces
+variable in
+.Xr rc.conf 5 .
+.Pp
 Special action will be taken when IPv6 TCP traffic is seen on a router,
 and routing table suggests to route it to
 .Nm

share/man/man4/stf.4

@@ -57,6 +57,18 @@ interface is necessary for site border router
 .Dq 6to4 router
 in the specification).
 .Pp
+Each
+.Nm
+interface is created at runtime using interface cloning.
+This is
+most easily done with the
+.Xr ifconfig 8
+.Cm create
+command or using the
+.Va cloned_interfaces
+variable in
+.Xr rc.conf 5 .
+.Pp
 Due to the way 6to4 protocol is specified,
 .Nm
 interface requires certain configuration to work properly.

share/man/man4/vlan.4

@@ -43,6 +43,18 @@ the IEEE 802.1Q standard into logical
 network interfaces, which allows routing/bridging between
 multiple VLANs through a single switch trunk port.
 .Pp
+Each
+.Nm
+interface is created at runtime using interface cloning.
+This is
+most easily done with the
+.Xr ifconfig 8
+.Cm create
+command or using the
+.Va cloned_interfaces
+variable in
+.Xr rc.conf 5 .
+.Pp
 To function, a
 .Nm
 interface must be assigned a parent interface and