Refs #14986. Add comment about building with openmp support.

buildconfig/Jenkins/buildscript

@@ -91,6 +91,9 @@ if [[ $USE_CLANG ]]; then
   fi
 fi
 
+#for openmp support on OS X run
+# `brew install llvm`
+# `ln -s /usr/local/opt/llvm/lib/libomp.dylib /usr/local/lib/libomp.dylib`
 if [[ $(uname) == 'Darwin' ]] ; then
   if [[ ${JOB_NAME} == *openmp* ]]; then
     export CC=/usr/local/opt/llvm/bin/clang