Add license to project

### Describe the bug
Currently, the project has no `LICENSE` file. although the modrinth page does list it as being GPL, it is good practice to create a license file.

### Log Files
N/A
### Mod Version, Modloader, and Minecraft Version
- Which version of the mod are you using?
N/A

- Fabric, Forge, NeoForge?
N/A

- Which Minecraft version?
N/A
