nethack/Contributing.md

If you are making a GitHub pull request for NetHack, please follow these guidelines:

1. The 50/72 Rule: Keep the subject line (the first line) under 50 characters for readability in git log --oneline. If you need a more detailed description (the body), wrap it at 72 characters.

2. Separate Subject from Body: Always include a blank line between the subject and the body. This helps Git tools correctly parse the message.