show proper command usage when there's no arguments

[asfimport]

parquet-tools command line currently does not show synopsis when no arguments are provided.

Reporter: Kaufman Ng / @coughman
Assignee: Kaufman Ng / @coughman

PRs and other links:

• PR #336

_{Note: This issue was originally created as PARQUET-584. Please see the migration documentation for further details.}

[asfimport]

Kaufman Ng / @coughman:
pull request: #336

[asfimport]

Ryan Blue / @rdblue:
Merged. Thanks for fixing this, @coughman!