add PATH to example crontab

crontab.example

@@ -1,3 +1,7 @@
+# supply all the paths the script needs to run
+PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+SHELL=/bin/bash
+
 # backup mail, once every 2 hours
 30 */2 * * * /root/backup/backupscript.sh -q -k 20 mail
 # backup userdirs