Clarify directory changelogs need to go into (#2638)

Author: martijnbastiaan

changelog/README.md

@@ -3,7 +3,7 @@ we now use a single file per change. Of course, if you feel adding an entry to
 the CHANGELOG would only pollute it, feel free to not make a file. To keep it
 somewhat manageable:
 
-* Create a changelog file: `touch $(date --iso-8601=seconds | tr : _)_my_change_message`
+* Create a changelog file: `touch changelog/$(date --iso-8601=seconds | tr : _)_my_change_message`
 * We collect these files for each release and put their messages in
   `CHANGELOG.md`. The files are subsequently deleted.
 * Messages should be valid Markdown