make it obvious that pre-automation/ is a directory

Author: TimidRobot

README.md

@@ -15,7 +15,7 @@ This project is currently being worked on as a Google Summer of Code (GSoC)
 project. The goal is to add automation of data gathering and report generation
 so that our reports quantifying the commons are never more than 3 months out of
 date. To prepare for this refactor, previous work was moved to
-[`pre-automation`](pre-automation/).
+[`pre-automation/`](pre-automation/).
 
 
 ## Code of conduct