update readme cmake requirement (#26)

README.md

@@ -11,13 +11,13 @@ tutorial and then moving on to the Intermediate tutorial.
 If you are running on an LC machine and would like to build locally, 
 be sure to do the following to build and run the tutorials:
 ```
-module load cmake/3.20.2
+module load cmake/3.23.1
 module load gcc/8.3.1
 module load cuda/11.2.0
 cmake -DENABLE_CUDA=On -DENABLE_OPENMP=Off -DCMAKE_CUDA_ARCHITECTURES=70 -DCMAKE_CUDA_COMPILER=/usr/tce/packages/cuda/cuda-11.2.0/bin/nvcc -DCUDA_TOOLKIT_ROOT_DIR=/usr/tce/packages/cuda/cuda-11.2.0 -DBLT_CXX_STD=c++14 -DCMAKE_BUILD_TYPE=Release -DRAJA_ENABLE_EXERCISES=On -DRAJA_ENABLE_OPENMP=Off -DCMAKE_CUDA_FLAGS=--extended-lambda -DCUDA_ARCH=sm_70 ../
 ```
 
-(Note: you need a cmake version greater than 3.19 and you need a more
+(Note: you need a cmake version greater or equal than 3.23.1 and you need a more
 recent gcc version which can handle c++14. For example, on the Lassen LC machine a cmake command like `cmake -DBLT_CXX_STD=c++14 -DCMAKE_CUDA_ARCHITECTURES=70 -DENABLE_CUDA=On -DCMAKE_CUDA_FLAGS="--expt-extended-lambda" ../` after loading appropriate cmake and gcc modules will work well.)
 
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