Update README.md

[christiansievers]

tiny typo fix

[RhetTbull]

@christiansievers thanks for this. The README is actually dynamically built as part of the release process. The typo you fixed is in osxphotos/tutorial.md. Please update the original in tutorial.md and re-submit the PR otherwise the fix will be overwritten when I next build the README.

[RhetTbull]

@all-contributors please add @christiansievers for docs

[allcontributors]

@RhetTbull

I've put up a pull request to add @christiansievers! 🎉

[christiansievers]

I added another commit, now with the correct file edited. Not sure if you can ignore the fix to the dynamically built file.

[RhetTbull]

Thanks!