Add comprehensive README documentation for iOS app

[Copilot]

Expand minimal README into structured documentation covering app overview, features, usage, and installation.

Changes

• Structure: Added standard sections (Overview, Features, How It Works, Purpose, Requirements, Installation, Usage, Privacy, License, Author)
• Features: Documented core capabilities (daily stress relief, smart counter system, emotion indicator, daily reset)
• User flow: Explained 5-step usage pattern from app launch to insight generation
• Metadata: Added iOS platform and MIT license badges
• Privacy: Clarified local-only data storage

The original description is preserved in the Description section while new sections provide actionable information for users and developers.

Original prompt

生成readme.md文件介绍：This is an iOS app called "Quitting Tomorrow." Simply put, the app allows users to release work-related stress daily by expressing their emotions. It features a button with a counter function. The logic is that if a user clicks the button too many times in a day, it indicates a strong desire to quit their job.

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