docs(changelog): add the range ring sonar pulses fragment for #1519

changelog.d/1519-range-ring-sonar-pulses.md

@@ -0,0 +1,6 @@
+- The Global Context range ring pulses like a sonar: three dim rings with a
+  soft inward glow grow from the subject to 250 km, and the ring flashes as
+  each one arrives. Flights, military aircraft and AIS vessels a pulse crosses
+  get a brief echo around their brackets. While a subject is shown, a parked
+  Contacts view repaints about 12 times a second. Under reduced motion there
+  are no pulses and the ring stays on screen (manjunath22466, #1519).