add news

Author: lorenzwalthert

NEWS.md

@@ -18,6 +18,8 @@
 
 - blank lines in function calls and headers are now removed, for the former only 
   when there are no comments before or after the blank line (#629, #630, #635).
+- speed improvement (~10%) when cache is activated because transformers are not 
+  captured as character anymore (#679).
 
 ## Minor changes and fixes