NEWS: Add entry for default target feature

NEWS

@@ -30,6 +30,10 @@ buildstream 1.3.1
     specific. Recommendation if you are building in Linux is to use the
     ones being used in freedesktop-sdk project, for example
 
+  o Running commands without elements specified will now attempt to use
+    the default targets defined in the project configuration.
+    If no default target is defined, all elements in the project will be used.
+
   o All elements must now be suffixed with `.bst`
     Attempting to use an element that does not have the `.bst` extension,
     will result in a warning.