Update Profiling Section in XNNPACK Delegate Docs (#3237)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3237

Updating Profiling Section of the docs

Main point is pointing the the SDK Profiling Tutorial on how to get XNNPACK profiling information

Reviewed By: metascroy, cccclai

Differential Revision: D56439491

fbshipit-source-id: 1d724ffae6d89e8769ea427cb37b4ec85fe3452f