docs: mention the existence of the toggles in the man page

doc/man/nano.1

@@ -257,6 +257,14 @@ separately (e.g.\& 'nano \-wS \-$').
 .BR \-a ", " \-b ", " \-e ", " \-f ", " \-g ", " \-j
 Ignored, for compatibility with Pico.
 
+.SH TOGGLES
+Many of the above options can be switched on and off also while
+\fBnano\fR is running.  For example, \fBM\-L\fR toggles the
+hard-wrapping of long lines, \fBM\-$\fR toggles soft-wrapping,
+\fBM\-#\fR toggles line numbers, \fBM\-P\fR the visibility of
+whitespace, \fBM\-M\fR the mouse, and \fBM\-X\fR the help lines.
+See at the end of the \fB^G\fR help text for a complete list.
+
 .SH INITIALIZATION FILE
 \fBnano\fP will read initialization files in the following order:
 the system's \fBnanorc\fP (if it exists), and then the user's