docs(nodejs): note CJS bundle and system-installed CLI requirements

Author: darthmolen

nodejs/README.md

@@ -850,6 +850,21 @@ try {
 - Node.js >= 18.0.0
 - GitHub Copilot CLI installed and in PATH (or provide custom `cliPath`)
 
+### CJS Bundles (esbuild, VS Code extensions)
+
+The SDK is ESM-only. When loaded in a CJS-shimmed environment (e.g., a VS Code extension bundled with `esbuild format:"cjs"`), `getBundledCliPath()` resolves the CLI by walking `node_modules`. The `@github/copilot` package **must be present in `node_modules` at runtime** — do not externalize or exclude it from your bundle.
+
+### System-installed CLI (winget, brew, apt)
+
+If you installed the Copilot CLI separately rather than relying on the SDK's bundled copy, `getBundledCliPath()` will not find it (it only searches `node_modules`). Pass `cliPath` explicitly instead:
+
+```typescript
+const client = new CopilotClient({
+    cliPath: '/usr/local/bin/copilot',   // macOS/Linux
+    // cliPath: 'C:\\path\\to\\copilot.exe', // Windows (winget, etc.)
+});
+```
+
 ## License
 
 MIT