[stzn/the-swift-programming-language-jp] Pull request opened: #517 [Concurrency] 全般的な内容の更新

[stzn/the-swift-programming-language-jp] Pull request closed: #517 [Concurrency] 全般的な内容の更新

[stzn/the-swift-programming-language-jp] Issue closed: #443 Concurrencyの改善

[stzn/the-swift-programming-language-jp] Pull request opened: #518 contributors readme action update