Adding a LICENSE file

[chroth]

This project solves a huge pain with working with next-i18next. Great work! But without a license file I don't think I can use it. Would be really nice if you wanted to add one. From the package.json it looks like you are open to licensing your project under the MIT license. You'd just need to add a license file, e.g. https://choosealicense.com/licenses/mit/