Add missing documentation for rate limit config

Currently we don't have documentation for the [appsettings.ip-rate-limiting.json](https://github.com/sia-digital/pibox/blob/main/example/src/PiBox.Example.Service/appsettings.ip-rate-limiting.json)
The functionality is provided by the following nuget package:  https://github.com/stefanprodan/AspNetCoreRateLimit

- [ ]  Add missing formation to the webhost documentation readme
