NEWS: Add note about breaking cache key change
diff --git a/NEWS b/NEWS
index b69e3c9..af362eb 100644
--- a/NEWS
+++ b/NEWS
@@ -19,6 +19,10 @@
 Plugins
 -------
 
+  o Cache keys will change for all elements that have defined the
+    `command-subdir` variable. This is the result of fixing a bug where this
+    variable was not included in the cache key correctly.
+
   o The `pip` element has been removed. Please use the one from bst-plugins-experimental