Fixed readme pointing to old markdown file

Author: daymxn

buildSrc/README.md

@@ -5,7 +5,7 @@ plugins and systems require a moderate amount of cognitive overhead to understan
 I thought it best to provide documentation for such systems. You can find the
 currently documented systems below:
 
-[Dackka Plugin](src/main/java/com/google/firebase/gradle/plugins/DackkaPlugin.md)
+[Dackka Plugin](src/main/java/com/google/firebase/gradle/plugins/DackkaPlugin.kt)
 
 
 * Note that this file currently only serves as a table of contents until sufficient documentation has been created.