Third party packages are normally not uploaded to the repo and will be downloaded when someone tries to compile your electron app (by running npm install). If no third party code is included in your repo, I think it will be ok for just adding a license file to it.
How I have done it-
Yes it is as simple as that, beside that you can License your app from GitHub repository it self
You can add a file(ThirdPartyLicense.txt) consisting all the licenses of dependencies and transitive dependencies in you main repository folder.
This method is used by all big projects example
Add credit for third party in your app credits ...
The requirement to credit the original author is intrinsic to basically each open-source license. Credits whom credit is due and usually the credits have to be retained and own changes indicated.
"I don't want people to make it closed-source in any way" is a strong statement - and IMHO a clear indicator that the MIT choice is not ideal: MIT allows ...
One possibility is the zLib License, which includes this requirement:
Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
It's true the zLib License is intended for software, but it still might suit your purposes in this case.
Full text of license:
(C) [year] [fullname]
It sounds like the game publisher doesn't want an open source license. As soon as the code is released under an open source license, anyone will be able to do what they like with the code, and that's going to mean that they lose all control as to what people do with their mechanics and graphics.
The graphics issue can actually be worked around by licensing ...