Missing License

Hello,

I am using your package indirectly through `InstantSearch-ios`. In my project I am using a tool to collect all licenses. Currently I have to exclude your project from the generation since it is missing a proper License file or any information about the license. It would be awesome if you can add a license file.

The issue names no specific file or test. First inspect the repository for existing license information and confirm which license applies; then add the requested license file. Done means the repository exposes a proper license that license-collection tooling can detect.

Written by the indexing model from the issue text.