MAINT: Add headers (Sourcery refactored)

[sourcery-ai]

Pull Request #11 refactored by Sourcery.

If you're happy with these changes, merge this Pull Request using the Squash and merge strategy.

NOTE: As code is pushed to the original Pull Request, Sourcery will
re-run and update (force-push) this Pull Request with new refactorings as
necessary. If Sourcery finds no refactorings at any point, this Pull Request
will be closed automatically.

See our documentation here.

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Review changes via command line

To manually merge these changes, make sure you're on the addHeaders branch, then run:

git fetch origin sourcery/addHeaders
git merge --ff-only FETCH_HEAD
git reset HEAD^

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