docs: add build instructions

[nguyenthuan155632]

Summary

Add a How to Build section to the main README so contributors can build TablePro without searching through contributor documentation.

The section documents the macOS and Xcode requirements, first-time static library setup, the unsigned Debug build command, the DerivedData app location, and the path to personal Apple-team signing instructions.

Verification

• Ran git diff --check
• Confirmed the personal-team signing link target exists
• Previously verified the documented unsigned Debug build command completes successfully

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Raise the documented Xcode requirement

This new top-level build section tells contributors that Xcode 15 is sufficient, but the checked-in project metadata is from a much newer Xcode (TablePro.xcodeproj/project.pbxproj has objectVersion = 77 and LastUpgradeCheck = 2640/CreatedOnToolsVersion = 26.x). In the scenario where a new contributor follows this README on Xcode 15, the documented xcodebuild -project TablePro.xcodeproj ... path cannot reliably load/build the current project before they ever reach the signing steps, so the prerequisite should match the project version actually required.

Useful? React with 👍 / 👎.

[datlechin]

Thank you.