Update android/README.md, how to build pytorch android from source (pytorch#92356)

`sh ./scripts/build_pytorch_android.sh` leads to
```
./scripts/build_pytorch_android.sh: 30: source: not found
```

Pull Request resolved: pytorch#92356
Approved by: https://github.com/soulitzer

Author: vfdev-5

android/README.md

@@ -66,7 +66,7 @@ For this you can use `./scripts/build_pytorch_android.sh` script.
 git clone https://github.com/pytorch/pytorch.git
 cd pytorch
 git submodule update --init --recursive
-sh ./scripts/build_pytorch_android.sh
+bash ./scripts/build_pytorch_android.sh
 ```
 
 The workflow contains several steps: