Add instructions to template/ios/Podfile for enabling hermes (#30461)

Summary:
Just thought I'd add these instructions so devs don't have to check the docs. Also, it makes iOS match Android with instructions in the configuration files
## Changelog
N/A (in my opinion)

Pull Request resolved: #30461

Test Plan: N/A (because not a code change)

Reviewed By: hramos

Differential Revision: D25309687

Pulled By: TheSavior

fbshipit-source-id: a1907089b9d2e7fe6f2498ce27129c3ae65f7c9a

template/ios/Podfile

@@ -6,7 +6,11 @@ platform :ios, '10.0'
 target 'HelloWorld' do
   config = use_native_modules!
 
-  use_react_native!(:path => config[:reactNativePath])
+  use_react_native(
+    :path => config[:reactNativePath],
+    # to enable hermes on iOS, change `false` to `true` and then install pods
+    :hermes_enabled => false
+  )
 
   target 'HelloWorldTests' do
     inherit! :complete