Update qc docs

Author: lucylq

docs/source/build-run-qualcomm-ai-engine-direct-backend.md

@@ -145,6 +145,7 @@ cmake .. \
     -DCMAKE_INSTALL_PREFIX=$PWD \
     -DEXECUTORCH_BUILD_SDK=ON \
     -DEXECUTORCH_BUILD_QNN=ON \
+    -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
     -DQNN_SDK_ROOT=$QNN_SDK_ROOT \
     -DCMAKE_TOOLCHAIN_FILE=$ANDROID_NDK/build/cmake/android.toolchain.cmake \
     -DANDROID_ABI='arm64-v8a' \