explain what bin/ij does in output of -h and --help

`bin/ij -h` isn't recognized as trigger for short usage information and causes output `IJ ERROR: file not found: -h` and the long usage information triggered with `bin/ij --help` should at least contain an explanation what the tool does. The current form `Usage: java org.apache.derby.tools.ij [-p propertyfile] [inputfile]` is sufficient for the short usage information imo.