Update README.md (pytorch#946)

Mention Cmake as a requirement to build the LLaMA app with Xcode

README.md

@@ -312,7 +312,8 @@ The following assumes you've completed the steps for [Setting up ExecuTorch](#se
 <summary>Deploying with Xcode</summary>
 
 #### Requirements
-- Xcode 15.0 or later
+- [Xcode](https://apps.apple.com/us/app/xcode/id497799835?mt=12/) 15.0 or later
+- [Cmake](https://cmake.org/download/) 3.19 or later
 - A development provisioning profile with the [`increased-memory-limit`](https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_developer_kernel_increased-memory-limit) entitlement.