How to add localized description for errors in Swift (Error protocol)

Hi everyone! I'm writing my app in Swift 3 and encountered a problem with localizing error messages. I have my own error type implementing the Error protocol:

enum MyError: Error {
    case networkError
    case invalidInput(String)
    case unknown
}

I want the user to see a clear message in their language when an error occurs. I know about NSLocalizedString, but I don't understand how to properly integrate it with Error. I tried doing this:

extension MyError: LocalizedError {
    var errorDescription: String? {
        switch self {
        case .networkError:
            return NSLocalizedString("Network error", comment: "Network error")
        case .invalidInput(let field):
            return NSLocalizedString("Invalid input in", comment: "Invalid input in")
        }
    }
}