7.5: update audio/midi docs re saving i/o between backends

include/connecting-audio-and-midi-devices.html

@@ -11,6 +11,12 @@
   Common sense and basic troubleshooting skills are needed when problems arise, and in the above example, one would have to go through the entire signal chain to ensure that each component was working as it should.
 </p>
 
+<p>
+  For some cases, Ardour eliminates possible I/O issues. One such case is
+  automatically saving I/O per device to sessions and restoring connections
+  when switching the backend, e.g. from ALSA to PulseAudio and vice versa.
+</p>
+
 <h2>Common Problems</h2>
 
 <p>