README: Clarify iOS requirements (#1023)

Clarify iOS requirements

Author: shoumikhin

README.md

@@ -24,7 +24,7 @@ torchchat is a small codebase showcasing the ability to run large language model
   - Linux (x86)
   - Mac OS (M1/M2/M3)
   - Android (Devices that support XNNPACK)
-  - iOS 17+ (iPhone 13 Pro+)
+  - iOS 17+ and 8+ Gb of RAM (iPhone 15 Pro+ or iPad with Apple Silicon)
 - Multiple data types including: float32, float16, bfloat16
 - Multiple quantization schemes
 - Multiple execution modes including: Python (Eager, Compile) or Native (AOT Inductor (AOTI), ExecuTorch)