Update readme to use the latest release. (#4406)

Summary:
Pull Request resolved: #4406

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Reviewed By: kirklandsign

Differential Revision: D60204312

fbshipit-source-id: ea424f29ae43847292bcddfb971616ad071e102d

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

@@ -44,9 +44,8 @@ Follow the [Setting Up ExecuTorch](https://pytorch.org/executorch/stable/getting
 tutorial to configure the basic environment:
 
 ```bash
-git clone -b release/0.2 https://github.com/pytorch/executorch.git
+git clone https://github.com/pytorch/executorch.git -b release/0.3 --recursive
 cd executorch
-git submodule update --init
 
 python3 -m venv .venv && source .venv/bin/activate