add mobile doc skeleton (#310)

Author: mikekgfb

docs/Android.md

@@ -0,0 +1,12 @@
+# Executing LLM models on Android
+
+Check out the [tutorial on how to build an Android app running your
+PyTorch models with
+Executorch](https://pytorch.org/executorch/main/llm/llama-demo-android.html),
+and give your torchat models a spin.
+
+![Screenshot](https://pytorch.org/executorch/main/_static/img/android_llama_app.png "Android app running Llama model")
+
+Detailed step by step in conjunction with ET Android build, to run on
+simulator for Android. `scripts/android_example.sh` for running a
+model on an Android simulator (on Mac)

docs/iOS.md

@@ -0,0 +1,15 @@
+# iOS
+
+Open the iOS Llama Xcode project at
+https://github.com/pytorch/executorch/tree/main/examples/demo-apps/apple_ios/LLaMA/LLaMA.xcodeproj
+in Xcode and click Run.  You will need to provide a provisioning
+profile (similar to what's expected for any iOS dev).
+
+Once you can run the app on you device,
+1 - connect the device to you Mac,
+2 - copy the model and tokenizer.bin to the iOS Llama app
+3 - select the tokenizer and model with the `(...)` control (bottom left of screen, to the left of the text entrybox)
+
+
+Detailed step by step in conjunction with ET iOS build, to run on
+simulator for iOS.