Improve executor_runner cmake instructions

Author: guangy10

backends/xnnpack/README.md

@@ -105,6 +105,7 @@ mkdir cmake-out
 cmake \
     -DCMAKE_INSTALL_PREFIX=cmake-out \
     -DCMAKE_BUILD_TYPE=Release \
+    -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
     -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \

docs/source/tutorial-xnnpack-delegate-lowering.md

@@ -154,6 +154,7 @@ mkdir cmake-out
 cmake \
     -DCMAKE_INSTALL_PREFIX=cmake-out \
     -DCMAKE_BUILD_TYPE=Release \
+    -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
     -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \

examples/xnnpack/README.md

@@ -38,6 +38,7 @@ mkdir cmake-out
 cmake \
     -DCMAKE_INSTALL_PREFIX=cmake-out \
     -DCMAKE_BUILD_TYPE=Release \
+    -DEXECUTORCH_BUILD_EXECUTOR_RUNNER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
     -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
     -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \