I'd like to do that as well, but I don't have many info about it. I will make some researches and notify you if I find something useful!

I'm in the same boat. I was checking the Creative Commons licenses, and this could be an option:

https://creativecommons.org/licenses/by-nc-nd/4.0/

CC BY-NC-ND 4.0 Deed

Attribution-NonCommercial-NoDerivs 4.0 International

You are free to:

1. Share — copy and redistribute the material in any medium or format
2. The licensor cannot revoke these freedoms as long as you follow the license terms.

Under the following terms:

1. Attribution — You must give appropriate credit , provide a link to the license, and indicate if changes were made . You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
2. NonCommercial — You may not use the material for commercial purposes .
3. NoDerivatives — If you remix, transform, or build upon the material, you may not distribute the modified material.
4. No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.

You can have different licenses for each different file/folder in your project. Github can generate license files for you as well, but it's good practice to put on your README.md all the licenses you have too, for example you can look at my repository to see how you can license everything correctly, just beware because my assets are all creative commons, so take care not to use the same licenses I did.

There are a bunch of open source licenses, the MIT is the simplest and easiest one to use, it just requires the users to keep the license file if they take your code. Another famous one is the GPL-2.0, which requires the user to also publish their work under the same license if they use your code. If you want to have full rights over your art and music, you should probably make them proprietary and write your legal notice with your conditions.