make it clear to which files the CC-BY-4.0 license applies

docs/LICENSE

 AsciiDoc documentation (c) by Sarah White, Dan Allen, and other contributors.
 
-Content in this repository is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.
+Content under this directory is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.
 
 You can find the complete text of this license at http://creativecommons.org/licenses/by/4.0/.