docs(changelog): add the perimeter size fragment for #1569

changelog.d/1569-perimeters-sub-acre-size.md

@@ -0,0 +1,3 @@
+- Show a fire perimeter under one acre at its reported size. The incident card
+  rounded WFIGS sizes to whole acres, so a 0.25-acre fire read "0 ac"
+  (Rudy Celekli, @rudycelekli, #1569).