Issue compiling the example program in Xcode 13.1

[metronome12]

I found an issue compiling the example program in Xcode 13.1.

The issue can be solved by adding the following to the dependencies section in the Package.swift file:

    .package(url: "https://github.com/Boilertalk/secp256k1.swift.git", from: "0.1.0"),
    .package(url: "git@github.com:apple/swift-nio-zlib-support.git", from: "1.0.0"),

I would have fixed it myself but don't think I have the ability to do a PR on the repo.