add link to info on file permissions

Author: TimidRobot

README.md

@@ -227,6 +227,13 @@ When run this way, the shared library (`scripts/shared.py`) provides easy access
 to all of the necessary paths and all of the modules managed by pipenv are
 available.
 
+In order for scripts to be run directly (as shown above), the script must be
+executable. For more information on making files executable, please see:
+[File Permissions - Foundational technologies — Creative Commons Open
+Source][file-perms].
+
+[file-perms]: https://opensource.creativecommons.org/contributing-code/foundational-tech/#file-permissions
+
 
 ### Static analysis