Add Tiercel to Swift networking

[Danie1s]

Add Tiercel to Swift.md under the networking section.

Tiercel is a pure Swift iOS download framework focused on background downloads, resumable transfers, relaunch recovery, and task management.

[Copilot]

Pull request overview

Adds Tiercel to the Swift networking resources list, expanding the repository’s curated Swift networking/download tooling references.

Changes:

• Add a Tiercel entry under 网络请求 in Swift.md.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Jinshishu]

这是来自QQ邮箱的假期自动回复邮件。   您好，我最近正在休假中，无法亲自回复您的邮件。我将在假期结束后，尽快给您回复。