fixup! README.md: Add a Windows-specific preamble

Visual Studio Code _just_ introduced a new, neat feature, where clicking
on a badge can open the repository really quickly, without having to
clone it (e.g. when fixing typos or things like that).

Let's add that badge to our README.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

README.md

@@ -1,6 +1,7 @@
 Git for Windows
 ===============
 
+[![Open in Visual Studio Code](https://open.vscode.dev/badges/open-in-vscode.svg)](https://open.vscode.dev/git-for-windows/git)
 [![Build status](https://github.com/git-for-windows/git/workflows/CI/PR/badge.svg)](https://github.com/git-for-windows/git/actions?query=branch%3Amaster+event%3Apush)
 [![Join the chat at https://gitter.im/git-for-windows/git](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/git-for-windows/git?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)