Add details of the source of the default word list to the documentation

[emystein]

I think it would be useful to see some detail / explanation of the source of the default word list in the official documentation.

My manager asked me what the source of the word list is and I can't answer that question without digging into the source code. I'm not saying it's invalid or a bad practice to check the source code, but it might be faster and useful to others to see those details right in the documentation.

Thanks,