Update README.md to include new build instructions.

Change-Id: I72ca67d3016c99682cfe745bfd74c722ea181a61


[ROCm/ROCR-Runtime commit: ee22d80760]

projects/rocr-runtime/README.md

@@ -15,7 +15,7 @@ A simple cmake-based system is available for building thunk. To build the runtim
 ```bash
     mkdir -p build
     cd build
-    cmake ..
+    cmake -DCMAKE_MODULE_PATH=../cmake_modules ..
     make
 ```