modify README

diff --git a/README.md b/README.md
index 1488ef8..f1f63db 100644
--- a/README.md
+++ b/README.md

@@ -91,6 +91,12 @@
 -DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
 ```
 
+To enable parallelization with OpenMP runtime, add the following flag to the command above:
+
+```shell
+-DLLVM_ENABLE_RUNTIMES=openmp
+```
+
 Run the following to ensure the MPACT compiler builds and runs correctly.
 
 ```shell