Since we're usually just appending lines to the file, it might make
sense to tell git to merge the file as union and not omit lines
that were missing on the branch if master has had them added.

source:
https://krlmlr.github.io/using-gitattributes-to-avoid-merge-conflicts/

Text from git docs:
https://git-scm.com/docs/gitattributes
> Run 3-way file level merge for text files, but take lines from both
> versions, instead of leaving conflict markers. This tends to leave the
> added lines in the resulting file in random order and the user should
> verify the result. Do not use this if you do not understand the
> implications.