[CI] Update AppVeyor status badge to use shields.io to comply to new GitHub policy for external images.

Author: LukasBanana

README.md

@@ -33,7 +33,7 @@ with Introduction, Hello Triangle Tutorial, and Extensibility Example with [GLFW
 
 | Platform | CI | D3D12 | D3D11 | Vulkan | OpenGL | Metal |
 |----------|:--:|:-----:|:-----:|:------:|:------:|:-----:|
-| <img src="docu/Icons/windows.svg" height="20" /> Windows | <p>[![MSVC16+ CI](https://github.com/LukasBanana/LLGL/actions/workflows/ci_windows.yml/badge.svg)](https://github.com/LukasBanana/LLGL/actions/workflows/ci_windows.yml)</p> <p>[![MSVC14 CI](https://ci.appveyor.com/api/projects/status/j09x8n07u3byfky0?svg=true)](https://ci.appveyor.com/project/LukasBanana/llgl)</p> | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | N/A |
+| <img src="docu/Icons/windows.svg" height="20" /> Windows | <p>[![MSVC16+ CI](https://github.com/LukasBanana/LLGL/actions/workflows/ci_windows.yml/badge.svg)](https://github.com/LukasBanana/LLGL/actions/workflows/ci_windows.yml)</p> <p>[![MSVC14 CI](https://img.shields.io/appveyor/build/LukasBanana/llgl?logo=appveyor&label=MS%20Windows)](https://ci.appveyor.com/project/LukasBanana/llgl)</p> | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | N/A |
 | <img src="docu/Icons/uwp.svg" height="20" /> UWP | [![UWP CI](https://github.com/LukasBanana/LLGL/actions/workflows/ci_uwp.yml/badge.svg)](https://github.com/LukasBanana/LLGL/actions/workflows/ci_uwp.yml) | :heavy_check_mark: | :heavy_check_mark: | N/A | N/A | N/A |
 | <img src="docu/Icons/linux.svg" height="20" /> GNU/Linux | [![GNU/Linux CI](https://github.com/LukasBanana/LLGL/actions/workflows/ci_linux.yml/badge.svg)](https://github.com/LukasBanana/LLGL/actions/workflows/ci_linux.yml) | N/A | N/A | :heavy_check_mark: | :heavy_check_mark: | N/A |
 | <img src="docu/Icons/macos.svg" height="20" /> macOS | [![macOS CI](https://github.com/LukasBanana/LLGL/actions/workflows/ci_macos.yml/badge.svg)](https://github.com/LukasBanana/LLGL/actions/workflows/ci_macos.yml) | N/A | N/A | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |