Add the changelog fragment for #1747

changelog.d/1747-vessels-every-frame.md

@@ -0,0 +1,5 @@
+- Move vessels every frame. Vessels between fixes, and live vessels a host
+  placement places, were redrawn at most every 250 ms with a frame asked for
+  once a second; they are now redrawn every frame, and the next frame is asked
+  for once the fastest drawn vessel will have moved half a pixel on screen
+  (Sameh Khamis, #1747).