[PyTorch Edge] Update iOS readme to use lite interpreter (#59841)

Summary:
Pull Request resolved: #59841

As lite interpreter moves to beta, it's recommended to let users start using it.
ghstack-source-id: 131766778

Test Plan: CI

Reviewed By: husthyc

Differential Revision: D29048350

fbshipit-source-id: 54d2ad09b4e9475304522c80b358647bcea79b14

ios/README.md

@@ -6,15 +6,15 @@
 PyTorch is now available via Cocoapods, to integrate it to your project, simply add the following line to your `Podfile` and run `pod install`
 
 ```ruby
-pod 'LibTorch'
+pod 'LibTorch-Lite'
 ```
 
 ### Import the library
 
 For Objective-C developers, simply import the umbrella header
 
 ```
-#import <LibTorch/LibTorch.h>
+#import <LibTorch-Lite.h>
 ```
 
 For Swift developers, you need to create an Objective-C class as a bridge to call the C++ APIs. We highly recommend you to follow the [Image Classification](https://github.com/pytorch/ios-demo-app/tree/master/PyTorchDemo) demo where you can find out how C++, Objective-C and Swift work together.