Update README.md

Add automated testing status badge for Linux.

Author: dtarditi

README.md

@@ -54,6 +54,8 @@ wiki](https://github.com/checkedc/checkedc-llvm-project/wiki).
 
 ## Automated testing status
 
+[![Checked C Clang CI Linux]](https://github.com/checkedc/workflows/actions/workflows/check-clang-linux.yml/badge.svg)](https://github.com/checkedc/workflows/actions/workflows/check-clang-linux.yml)
+
 [![Checked C Clang CI [MacOS]](https://github.com/checkedc/workflows/actions/workflows/checkedc-clang-macos.yml/badge.svg)](https://github.com/checkedc/workflows/actions/workflows/checkedc-clang-macos.yml)
 
 [![Checked C Clang CI [WINDOWS]](https://github.com/checkedc/workflows/actions/workflows/check-clang-windows.yml/badge.svg)](https://github.com/checkedc/workflows/actions/workflows/check-clang-windows.yml)