This PR adds a copy of the lottie-ios privacy manifest to this repo.

The binary Lottie.xcframework includes a privacy manifest. In airbnb/lottie-ios#2364 (reply in thread), we've confirmed this is detected and consumed properly by Xcode. There's been some confusion about this though, since it's not obvious and not documented.

This PR documents how the privacy manifest integration works, and adds a copy of it to this repo for convenience. I also imported a few other relevant sections from lottie-ios's README.