Copilot CLI Tutorial #4 - Custom Instructions

A tutorial on using GitHub Copilot CLI's custom instructions feature to guide Copilot's code generation decisions. It covers creating a `.github/copilot-instructions.md` file using the `init` command, which automatically scans the codebase to detect architecture, libraries, and coding styles. The demo uses an Astro + React project, showing how Copilot picks up conventions like CSS modules for React components and client-visible directives, then applies them consistently in subsequent prompts.