funclang series5: Added some comments in test file.

funclang-taddeus/series5/test_expr.ml

 #use "ass13.ml"
 
+(* Note: to run this test, run 'ocaml test_expr.ml' in the command line. This
+ * will print a list of SUCCESS/FAILURE lines (actually only SUCCESS for the
+ * current tests, but feel free to add some more challenging tests. *)
 let test tested_method e expect yield =
     if yield = expect then
         print_endline "SUCCESS"