Add new features to the documentation with limitations

[maordavidov]

Add the new resolve all namespaces and proxy external private destinations features to the documentation.

Limitations:

1. Proxy doesn't support the same port multiple times, even on different dns
2. When using a proxy without graceful shutdown, the hosts file will have the real DNS records as proxy. Assuming the user can reach the DNS from his laptop as well (for example - Google PubSub or AWS SQS), the user will manually need to delete the host OR run the kubetunnel and gracefully shut down.
3. When using all namespaces flag, the service namespace will be the main DNS. In order to resolve all other namespaces the user will need to use a fully qualified URL.