Answering here even if it’s very old because this is something I stumbled on google looking for the answer myself.
I found the solution via this post: https://forums.unrealengine.com/deve…kage-txt-files
It’s a bit tricky to find. But all you have to do is go to the project’s packaging setting’s:
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Then you have to expand the first section to find the “Additional Non-Asset Directories to Package” option.
There you just add the directory with the custom/non-asset files you want to include in the package.
It’s really easy. You just have to know about it (and find it). 
