Fix missing parenthesis

notes/guidelines.md

 Otherwise use `think()` instead.
 
 If you want to make your script "user-friendly" (like babbling about
-what it's doing, consider setting `FFOO_VERBOSE` to true in header of
+what it's doing), consider setting `FFOO_VERBOSE` to true in header of
 your script (and implementing `-q|--quiet` to tun it off).