add news bullet

NEWS.md

@@ -1,5 +1,17 @@
 # ggplot2 (development version)
 
+* `coord_radial()` is a successor to `coord_polar()` with more customisation 
+  options. `coord_radial()` can:
+
+  * integrate with the new guide system via a dedicated `guide_axis_theta()` to
+    display the angle coordinate.
+  * in addition to drawing full circles, also draw circle sectors by using the 
+    `end` argument.
+  * avoid data vanishing in the center of the plot by setting the `donut` 
+    argument.
+  * adjust the `angle` aesthetic of layers, such as `geom_text()`, to align 
+    with the coordinate system using the `rotate_angle` argument.
+
 * By default, `guide_legend()` now only draws a key glyph for a layer when
   the value is is the layer's data. To revert to the old behaviour, you
   can still set `show.legend = c({aesthetic} = TRUE)` (@teunbrand, #3648).