Add NuGet version badge and link to package list in README

Make it easier for readers who just want to install the package quickly to spot NuGet availability without scrolling to the full package table.

Author: shimat

README.md

@@ -1,5 +1,7 @@
 ![opencvsharp](https://socialify.git.ci/shimat/opencvsharp/image?description=1&forks=1&language=1&owner=1&pattern=Plus&stargazers=1&theme=Light)
 
+[![NuGet](https://img.shields.io/nuget/v/OpenCvSharp5.svg?label=NuGet%3A%20OpenCvSharp5)](https://www.nuget.org/packages/OpenCvSharp5/)
+
 [![GitHub Actions Windows Status](https://github.com/shimat/opencvsharp/actions/workflows/windows.yml/badge.svg)](https://github.com/shimat/opencvsharp/actions/workflows/windows.yml)  [![GitHub Actions Docker Test Status](https://github.com/shimat/opencvsharp/actions/workflows/docker-test-ubuntu.yml/badge.svg)](https://github.com/shimat/opencvsharp/actions/workflows/docker-test-ubuntu.yml)  [![GitHub Actions manylinux Status](https://github.com/shimat/opencvsharp/actions/workflows/manylinux.yml/badge.svg)](https://github.com/shimat/opencvsharp/actions/workflows/manylinux.yml)  [![GitHub Actions Wasm Status](https://github.com/shimat/opencvsharp/actions/workflows/wasm.yml/badge.svg)](https://github.com/shimat/opencvsharp/actions/workflows/wasm.yml) [![GitHub Actions macOS Status](https://github.com/shimat/opencvsharp/actions/workflows/macos.yml/badge.svg)](https://github.com/shimat/opencvsharp/actions/workflows/macos.yml) [![GitHub license](https://img.shields.io/github/license/shimat/opencvsharp.svg)](https://github.com/shimat/opencvsharp/blob/master/LICENSE) 
 
 OpenCvSharp is a cross-platform .NET wrapper for OpenCV, providing a rich set of image processing and computer vision functionality.
@@ -53,7 +55,7 @@ dotnet add package OpenCvSharp5.runtime.osx.x64
 dotnet add package OpenCvSharp5.runtime.osx.arm64
 ```
 
-For more installation options, see the [Installation](#installation) section below.
+For more installation options, see the [Installation](#installation) section below, or the full [NuGet package list](#nuget).
 
 ## Features
 * OpenCvSharp is modeled on the native OpenCV C/C++ API style as much as possible.