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

We're now using the default branch name `main`.

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

Author: dscho

README.md

@@ -2,7 +2,7 @@ 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)
+[![Build status](https://github.com/git-for-windows/git/workflows/CI/PR/badge.svg)](https://github.com/git-for-windows/git/actions?query=branch%3Amain+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)
 
 This is [Git for Windows](http://git-for-windows.github.io/), the Windows port