[v0.20] Show examples to disable backends separately

build.sh

@@ -13,6 +13,12 @@ cd build/
 # for example:
 # cmake -DCMAKE_CUDA_COMPILER=/usr/local/cuda/bin/nvcc -DCMAKE_CUDA_COMPILER_TOOLKIT_ROOT=/usr/local/cuda/ ..
 
+# In case you want to explicitely disable a backend, you can:
+# Disable CUDA backend:
+# cmake -DENABLE_CUDA_BACKEND=OFF ..
+# Disable Intel backend:
+# cmake -DENABLE_INTEL_BACKEND=OFF ..
+
 cmake ..
 make -j$(nproc)
 cd -