Mention string expansions for environment variables in changelog

CHANGES.txt

@@ -33,6 +33,10 @@ Next release
   send it to its whole process group instead to take care of possible
   children as well and not leave them behind.  Patch by Samuele Pedroni.
 
+- Environment variables may now be used in the configuration file
+  for options that support string expansion.  Patch by GitHub user
+  "silver-".
+
 - Fixed a race condition where supervisord might not act on a signal sent
   to it.  Thanks to Adar Dembo for reporting the issue and supplying the
   initial patch.