[docs] update badges in README (#7057)

* [docs] update badges in README

* Update README.md
Co-authored-by: Oliver Borchert <oliver.borchert@quantco.com>

---------
Co-authored-by: Oliver Borchert <oliver.borchert@quantco.com>

README.md

@@ -3,9 +3,11 @@
 Light Gradient Boosting Machine
 ===============================
 
+[![C++ GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/cpp.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/cpp.yml)
 [![Python-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/python_package.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/python_package.yml)
 [![R-package GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/r_package.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/r_package.yml)
 [![CUDA Version GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/cuda.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/cuda.yml)
+[![SWIG Wrapper GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/swig.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/swig.yml)
 [![Static Analysis GitHub Actions Build Status](https://github.com/microsoft/LightGBM/actions/workflows/static_analysis.yml/badge.svg?branch=master)](https://github.com/microsoft/LightGBM/actions/workflows/static_analysis.yml)
 [![Azure Pipelines Build Status](https://lightgbm-ci.visualstudio.com/lightgbm-ci/_apis/build/status/Microsoft.LightGBM?branchName=master)](https://lightgbm-ci.visualstudio.com/lightgbm-ci/_build/latest?definitionId=1)
 [![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/1ys5ot401m0fep6l/branch/master?svg=true)](https://ci.appveyor.com/project/guolinke/lightgbm/branch/master)