How to implement read receipt and typing indicator in IOS Chime Chat SDK

### What demo do you have issue with?

*For example: I'm trying to setup the meeting demo app.*

### How can the documentation be improved to help your use case?

*For example: Include a section on how to configure a demo CloudFormation resources.*

### What documentation have you looked at so far?

*For example: README.md, etc.*

The issue names no files, tests, or entry points. Start by identifying the iOS Chat SDK documentation and the expected read-receipt and typing-indicator use cases. Done means the documentation explains how to implement both behaviors for this use case.

Written by the indexing model from the issue text.