Update README.md

Signed-off-by: Haonan Yang <[email protected]>

Author: haonanya1

README.md

@@ -68,7 +68,7 @@ make all -j`nproc`
 
 ##### Preferred LLVM version
 
-By default, opencl-clang's cmake script is searching for LLVM 12.0.0. You can
+By default, opencl-clang's cmake script is searching for LLVM 13.0.0. You can
 override target version of LLVM by using the `PREFERRED_LLVM_VERSION` cmake
 option: