Add English documentation and getting started guide

[Copilot]

The project lacked English documentation for international developers. Chinese documentation exists (hu.md, ai.md) but no onboarding guide for English speakers.

Changes

• GETTING_STARTED.md: Comprehensive guide covering installation, API usage, card numbering system, and lookup table mechanics
• README.md: Added English overview, quick start examples, feature highlights, and documentation links
• .gitignore: Excludes Maven build artifacts

Usage Example

// Load lookup tables
HuTable.load(Files.readAllLines(Paths.get("majiang_clien_normal.txt")));
HuTableFeng.load(Files.readAllLines(Paths.get("majiang_clien_feng.txt")));
HuTableJian.load(Files.readAllLines(Paths.get("majiang_clien_jian.txt")));

// Check win conditions
boolean canWin = HuUtil.isHu(cards, gui);
List<Integer> tingCards = HuUtil.isTing(cards, gui);

// AI recommendations
int discard = AIUtil.outAI(cards, gui);

The library provides Mahjong win detection and AI algorithms using pre-computed lookup tables for performance.

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