In the Public folder of your mod, create the path to where Data.txt should go:
Public\[mod]\Stats\Generated\Data\
And then place Data.txt in that Data folder.
You can run "mkdir Stats\Generated\Data" from the command prompt, once you've changed the current directory to your mod's Public directory, to create all folders at once. Or, you can create those folders one-by-one.
That said, your Data.txt should contain only the keys you change, so that you're not overriding all of the other values, if they have been modified by anyone else for their mods.
For example, if I wanted to add Data.txt to my mod, I'd copy and modify Data.txt at the following path:
Data\Public\RivellonUnleveled_01f15813-ccc4-4e56-9e8a-1ace88b97a13\Stats\Generated\Data\Data.txt