First cut at adding FST4, FST4W to the User Guide.

doc/user_guide/en/tutorial-example6.adoc

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+FST4W has significant advantages over WSPR for use on the 2200 and 630
+m bands.  As for WSPR, the default Rx Freq is 1500 Hz and F Tol is
+100 Hz, so the active decoding range 1400 to 1600 Hz.  However, for added
+flexibility you can select different center frequencies and F Tol values.
+We expect that usage conventions will soon be established for FST4 activity on 2200 and 630 m.
+
+A new drop-down control below F Tol offers a round-robin mode for
+scheduling FST4W transmissions:
+
+image::FST4W_RoundRobin.png[align="center"]
+
+If three operators agree in advance to select the options 1/3, 2/3,
+and 3/3, for example, their FST4W transmissions will occur in a fixed
+sequence with no two stations transmitting simultaneously.  Sequence 1
+is the first sequence after 00:00 UTC.  For WSPR-like scheduling
+behavior, you should select Random with this control.