better message for testing wrapper

Author: remzi-arpacidusseau

initial-xv6/test-getreadcount.sh

@@ -1,7 +1,9 @@
 #! /bin/bash
 
 if ! [[ -d src ]]; then
-    echo "src dir does not exist"
+    echo "The src/ dir does not exist."
+    echo "Your xv6 code should be in the src/ directory"
+    echo "to enable the automatic tester to work."
     exit 1
 fi