cacdia/c-starter

AI Summary: Add a `.github/copilot-instructions.md` file to the C starter project repository, containing concise instructions for GitHub Copilot to follow, ensuring consistent code style and conventions. This involves writing clear instructions, enabling custom instructions in Copilot settings (VS Code and GitHub), and validating functionality across different interaction types.

AI Summary: Implement DevContainer support for a C project in VSCode, creating a `.devcontainer` directory with a `devcontainer.json` file specifying necessary configurations, a `Dockerfile` (if needed), and listing useful VSCode extensions. The goal is to provide a standardized and readily usable development environment.