Add extension readme file

Author: lszomoru

extensions/git-base/README.md

@@ -0,0 +1,20 @@
+# Git static contributions and remote repository picker
+
+**Notice:** This extension is bundled with Visual Studio Code. It can be disabled but not uninstalled.
+
+## Features
+
+Git static contributions and remote repository picker.
+
+## API
+
+The Git extension exposes an API, reachable by any other extension.
+
+1. Copy `src/api/git-base.d.ts` to your extension's sources;
+2. Include `git-base.d.ts` in your extension's compilation.
+3. Get a hold of the API with the following snippet:
+
+	```ts
+	const gitBaseExtension = vscode.extensions.getExtension<GitBaseExtension>('vscode.git-base').exports;
+	const git = gitBaseExtension.getAPI(1);
+	```