Added a screenshot for MIDI patch change. Solves issue #7362.

include/patch-change.html

@@ -1,4 +1,9 @@
 
+<figure class="right">
+  <img src="/images/patch_change.png" alt="A patch change in a MIDI region"/>
+  <figcaption>A patch change in a MIDI region</figcaption>
+</figure>
+
 <p>
   A <dfn>patch change</dfn> is Ardour's description for a combination
   of MIDI program change and bank select messages, that (typically)
@@ -7,7 +12,8 @@
 </p>
 <p>
   Patch changes are shown within MIDI regions as small rectangles or
-  <dfn>flags</dfn>, as shown below:
+  <dfn>flags</dfn>, with a vertical line showing where in the region
+  (hence "when") this patch change happens.
 </p>
 
 <h2>Inserting Patch Changes</h2>
@@ -51,4 +57,3 @@
 <p class=fixme>
   Add content
 </p>
-