(windbg) Add README w/ note about unlisting pkg

Author: pauby

unlisted/windbg/README.md

@@ -0,0 +1,5 @@
+# [Windows Standalone Debugging Tools](https://chocolatey.org/packages/windbg)
+
+The Windows Debugging Tools now [require use of the Windows SDK to install as a standalone tool](https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/#install-debugging-tools-for-windows). There are many Windows SDK packages in the [Chocolatey Community Repository for different versions of Windows](https://community.chocolatey.org/packages?q=debugging+tools).
+
+This package is would be deprecated in favour of these Windows SDK packages. However, as there are many and they apply to different Windows versions, there isn't one in particular that we deprecate against. The package was unlisted as the download locations were removed and the package is now broken.