apple-sdk sources are hard to find

https://crates.io/crates/apple-sdk links here as the source repository. However, the apple-sdk sources are nowhere to be found in this repo. That looks rather suspicious.

I eventually found them in https://github.com/indygreg/apple-platform-rs/tree/main/apple-sdk/. It'd be good to update the metadata on crates.io as well to avoid unnecessary confusion.

Start by inspecting the apple-sdk crate metadata and the repository files that define its crates.io package information. Update the source-repository link to the apple-platform-rs apple-sdk directory, then verify that the published metadata points contributors to the correct sources.

Written by the indexing model from the issue text.