Use absolute path on cmake parameter

Update build instructions in README.md to use absolute path on cmake
parameter, CMAKE_MODULE_PATH. Relative path causes build error. Tested
on cmake 3.5.1 ans cmake 3.5.2.

Change-Id: I1b8e8deb9f4941580580be8087a94655ae155d02
Signed-off-by: Amber Lin <Amber.Lin@amd.com>

README.md

@@ -10,12 +10,12 @@ https://github.com/RadeonOpenCompute/ROCK-Radeon-Open-Compute-Kernel-Driver
 
 #### Building the Thunk
 
-A simple cmake-based system is available for building thunk. To build the runtime from the the ROCT-Thunk-Interface directory, execute:
+A simple cmake-based system is available for building thunk. To build the thunk from the the ROCT-Thunk-Interface directory, execute:
 
 ```bash
     mkdir -p build
     cd build
-    cmake -DCMAKE_MODULE_PATH=../cmake_modules ..
+    cmake -DCMAKE_MODULE_PATH=${PWD}/../cmake_modules ..
     make
 ```