Fix the mklink command in README.md (#3820)

The `mklink /d` creates a directory symbolic link. As here we need a file symbolic link, the `/d` switch must not be used.

See `mklink` documentation: https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/mklink

README.md

@@ -51,7 +51,7 @@ ln -s ../../config/pre-push-recommended.sh .git/hooks/pre-push
 ```
 or for Windows run this command with administrative privileges:
 ```sh
-mklink /d .git\hooks\pre-push ..\..\config\pre-push-recommended.sh
+mklink .git\hooks\pre-push ..\..\config\pre-push-recommended.sh
 ```
 
 To push without running the pre-push hook (e.g. doc updates):