Help: Add notes for topic 'makefile-DELETE_ON_ERROR'

Help/release/dev/makefile-DELETE_ON_ERROR.rst

@@ -0,0 +1,7 @@
+makefile-DELETE_ON_ERROR
+------------------------
+
+* The Makefile generators now add ``.DELETE_ON_ERROR`` to the
+  makefiles that contain the actual build rules for files on disk.
+  This tells GNU make to remove rule outputs when their recipe
+  modifies an output but fails.