Add RAJA CUDA build instructions

Author: tomdeakin

README.md

@@ -53,9 +53,12 @@ Building RAJA
 
 We use the following command to build RAJA using the Intel Compiler.
 ```
-cmake ../../ -DCMAKE_INSTALL_PREFIX=<prefix> -DCMAKE_C_COMPILER=icc -DCMAKE_CXX_COMPILER=icpc -DRAJA_PTR="RAJA_USE_RESTRICT_ALIGNED_PTR" -DCMAKE_BUILD_TYPE=ICCBuild -DRAJA_ENABLE_TESTS=Off
+cmake .. -DCMAKE_INSTALL_PREFIX=<prefix> -DCMAKE_C_COMPILER=icc -DCMAKE_CXX_COMPILER=icpc -DRAJA_PTR="RAJA_USE_RESTRICT_ALIGNED_PTR" -DCMAKE_BUILD_TYPE=ICCBuild -DRAJA_ENABLE_TESTS=Off
+```
+For building with CUDA support, we use the following command.
+```
+cmake .. -DCMAKE_INSTALL_PREFIX=<prefix> -DRAJA_PTR="RAJA_USE_RESTRICT_ALIGNED_PTR" -DRAJA_ENABLE_CUDA=1 -DRAJA_ENABLE_TESTS=Off
 ```
-
 
 Results
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