Needs to tell about --help

[vlm]

Pronk needs to tell the user about --help. The current message is cryptic.

[vlm@nala:~/work/github/third-party/pronk (master)]> pronk
Requires at least 1 arguments, got 0
[vlm@nala:~/work/github/third-party/pronk (master)]> 

[bos]

This is fixed by a change to the statistics package: haskell/statistics@a293324