pkg new: clarify 'module+ main' and 'module+ test' purpose

- edit the comments, thanks to John B Clements and Alex Gian and Alex McLin
  and Phil McGrath
- add simple example code

racket/collects/pkg/private/new.rkt

@@ -207,13 +207,29 @@ EOS
 
 ;; Code here
 
+
+
 (module+ test
-  ;; Tests to be run with raco test
-  )
+  ;; Any code in this `test` submodule runs when this file is run using DrRacket
+  ;; or with `raco test`. The code here does not run when this file is
+  ;; required by another module.
+
+  (check-equal? (+ 2 2) 4))
 
 (module+ main
-  ;; Main entry point, executed when run with the `racket` executable or DrRacket.
-  )
+  ;; (Optional) main submodule. Put code here if you need it to be executed when
+  ;; this file is run using DrRacket or the `racket` executable.  The code here
+  ;; does not run when this file is required by another module. Documentation:
+  ;; http://docs.racket-lang.org/guide/Module_Syntax.html#%28part._main-and-test%29
+
+  (require racket/cmdline)
+  (define who (box "world"))
+  (command-line
+    #:program "my-program"
+    #:once-each
+    [("-n" "--name") name "Who to say hello to" (set-box! who name)]
+    #:args ()
+    (printf "hello ~a~n" (unbox who))))
 
 EOS
 )))