Lack of documentation in 'crosswords.py'

[AlkisPis]

Re: https://github.com/python-constraint/python-constraint/tree/master/examples/crosswords/crossword.py

The script says "Usage: crosswords.py <maskfile> <wordsfile>". OK, one can figure out what the 'maskfile' is, based on the .mask files in the same folder with 'crosswords.py', altghough letting someone guessing is not the ideal way to present a code. But what about the 'wordsfile'? Here, one cannot even guess what this is all about. Neither is this explained elsewhere in the package.