Merge pull request bitcoin#839 from pengpengliu/master

BIP39: Add swift implementation

Author: luke-jr

bip-0039.mediawiki

@@ -168,6 +168,7 @@ Rust:
 Swift:
 * https://github.com/CikeQiu/CKMnemonic
 * https://github.com/yuzushioh/WalletKit
+* https://github.com/pengpengliu/BIP39
 * https://github.com/matter-labs/web3swift/blob/develop/Sources/web3swift/KeystoreManager/BIP39.swift
 * https://github.com/zcash-hackworks/MnemonicSwift