Fix Nethack General Public License Description

[fairfield-programming-bot]

Hello there!

When we started the Openlist, we added hundreds of licenses. Our problem? Most don't have great descriptions. If you would like to fix our description for the Nethack General Public License, leave a comment below and we will assign the issue to you.

Thank you for the help,
The FPA

P.S. here's the location of the Nethack General Public License.