Create copilot-instructions.md (#3109)

Author: msyyc

.github/copilot-instructions.md

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+# Copilot Instructions
+
+This document serves as an index to task-specific instructions for GitHub Copilot.
+
+## Install and Build
+
+- Packages are located in the `packages` folder
+- Use `pnpm` as the package manager
+- Use `pnpm install` to install dependencies
+- Use `pnpm build` to build every package
+- Use `pnpm format` under each subfolder of `packages` folder to format all files
+
+## Describing changes
+
+- Repo use `@chronus/chronus` for changelogs
+- Use `pnpm change add` to add a change description for the touched packages
+- Types of changes are described in `.chronus/config.yaml`