Mention the optional availability of the conn=sn=<serno> format to
select one of several connected devices.
$ sigrok-cli --driver <somedriver>:conn=vxi/<ipaddr> ...
$ sigrok-cli --driver <somedriver>:conn=usbtmc/<bus>.<addr> ...
+Individual device drivers _may_ implement additional semantics for the
+conn= specification, which would not apply to other drivers, yet can be
+rather useful for a given type of device.
+
+ $ sigrok-cli --driver <somedriver>:conn=sn=<serno>
+
Specifying serial port parameters
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