Add badges for GitHub Actions

Author: aafulei

README.md

@@ -1,5 +1,9 @@
 # Today
 
+[![Check](https://github.com/aafulei/cpp-today/actions/workflows/check.yml/badge.svg)](https://github.com/aafulei/cpp-today/actions/workflows/check.yml)
+[![Build](https://github.com/aafulei/cpp-today/actions/workflows/build.yml/badge.svg)](https://github.com/aafulei/cpp-today/actions/workflows/build.yml)
+[![Test](https://github.com/aafulei/cpp-today/actions/workflows/test.yml/badge.svg)](https://github.com/aafulei/cpp-today/actions/workflows/test.yml)
+
 A simple C++ program that prints the current date in the `YY/MM/DD = Www`
 format.