TBF man page fix (tbf is not classless)

TBF is not classless qdisc. man page corrected, added example
describing the use of inner qdisc
Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>

man/man8/tc-tbf.8

@@ -21,7 +21,7 @@ bytes/cell
 burst is also known as buffer and maxburst. mtu is also known as minburst.
 .SH DESCRIPTION
 
-The Token Bucket Filter is a classless queueing discipline available for
+The Token Bucket Filter is a classful queueing discipline available for
 traffic control with the 
 .BR tc (8)
 command.
@@ -121,9 +121,17 @@ To attach a TBF with a sustained maximum rate of 0.5mbit/s, a peakrate of 1.0mbi
 a 5kilobyte buffer, with a pre-bucket queue size limit calculated so the TBF causes
 at most 70ms of latency, with perfect peakrate behaviour, issue:
 .P
-# tc qdisc add dev eth0 root tbf rate 0.5mbit \\
+# tc qdisc add dev eth0 handle 10: root tbf rate 0.5mbit \\
   burst 5kb latency 70ms peakrate 1mbit       \\
   minburst 1540
+.P
+To attach an inner qdisc, for example sfq, issue:
+.P
+# tc qdisc add dev eth0 parent 10:1 handle 100: sfq
+.P
+Without inner qdisc TBF queue acts as bfifo. If the inner qdisc is changed
+the limit/latency is not effective anymore.
+.P
 
 .SH SEE ALSO
 .BR tc (8)