add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 (development version)
 
+* `annotation_borders()` replaces the now-deprecated `borders()` 
+  (@teunbrand, #6392)
 * `position_fill()` avoids stacking observations of zero (@teunbrand, #6338)
 * New `layer(layout)` argument to interact with facets (@teunbrand, #3062)
 * New `stat_connect()` to connect points via steps or other shapes