Currently the license for this mod technically forbids forking or contributing. (All rights reserved is the same as no license) I recommend adding an open-source license, choosealicense.com can help you pick, but i personally recommend the MIT license.

I am not comfortable with an open source license, especially after the sodium reupload controversy.
If people want explicit permission for anything they can feel free to ask, generally most things are fine.

If you do not want to use an existing open-source license, i would still encourage adding to the license file what is/isn't allowed (contributions, forks, distribution of forks, modifications, etc.)

You basically just write what is/isnt allowed there, there isnt really any specific example i can give, it's the same as making your own license.

without a working example I don't feel like making something on the spot

If your main concern is with people re-uploading your work, there are licenses which require others to credit you (and retain the license on any copies they make), such as the GNU AGPL.