[docs]: add use cases section to the readme

[legomushroom]

The use cases section in readme will help new users to understand how the gh net can be used and what are the target usage scenarios are.

This section may include:

• use case for working with remote/on-prem resource hosted inside developer VPN from a Codespace (aka network gateway)
• use case for routing from a Codespace to local machine (aka reverse network forwarding)
• use case for flashing/programming/debugging embedded devices connected to local machine from a Codespace