Update demo app readme. (#5962)

Summary:
Pull Request resolved: #5962

.

Reviewed By: kirklandsign

Differential Revision: D64016159

fbshipit-source-id: 31c453ce453fa66228baae977ccbd02b24dddbcc

Author: shoumikhin

examples/demo-apps/apple_ios/ExecuTorchDemo/README.md

@@ -44,11 +44,13 @@ Follow the [Setting Up ExecuTorch](https://pytorch.org/executorch/stable/getting
 tutorial to configure the basic environment:
 
 ```bash
-git clone https://github.com/pytorch/executorch.git -b release/0.3 --recursive
+git clone https://github.com/pytorch/executorch.git --depth 1 --recurse-submodules --shallow-submodules
 cd executorch
 
 python3 -m venv .venv && source .venv/bin/activate
 
+pip install --upgrade cmake pip setuptools wheel
+
 ./install_requirements.sh --pybind coreml mps xnnpack
 ```
 
@@ -74,13 +76,15 @@ Export the MobileNet v3 model with Core ML, MPS and XNNPACK backends, and move
 the exported model to a specific location where the Demo App will pick them up:
 
 ```bash
-python3 -m examples.portable.scripts.export --model_name="mv3"
-python3 -m examples.apple.coreml.scripts.export --model_name="mv3"
-python3 -m examples.apple.mps.scripts.mps_example --model_name="mv3"
-python3 -m examples.xnnpack.aot_compiler --delegate --model_name="mv3"
+MODEL_NAME="mv3"
+
+python3 -m examples.portable.scripts.export --model_name="$MODEL_NAME"
+python3 -m examples.apple.coreml.scripts.export --model_name="$MODEL_NAME"
+python3 -m examples.apple.mps.scripts.mps_example --model_name="$MODEL_NAME"
+python3 -m examples.xnnpack.aot_compiler --model_name="$MODEL_NAME" --delegate
 
 mkdir -p examples/demo-apps/apple_ios/ExecuTorchDemo/ExecuTorchDemo/Resources/Models/MobileNet/
-mv mv3*.pte examples/demo-apps/apple_ios/ExecuTorchDemo/ExecuTorchDemo/Resources/Models/MobileNet/
+mv "$MODEL_NAME*.pte" examples/demo-apps/apple_ios/ExecuTorchDemo/ExecuTorchDemo/Resources/Models/MobileNet/
 ```
 
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