[DOC] Update doc to reflect thread sampling logic required for tracing integration on

Update the docs to include this:

Walltime profiling is required to have [thread sampling logic changed with the tracing integration on](https://github.com/grafana/pyroscope-dotnet/blob/2a33bd7a949960070aa9496466c70b044b4558b7/profiler/src/ProfilerEngine/Datadog.Profiler.Native/StackSamplerLoop.cpp#L172). However, this information is not included in the docs.

In the docs, walltime profiling is only mentioned in the .NET SDK: https://grafana.com/docs/pyroscope/latest/configure-client/language-sdks/dotnet/#dynamic-control

The trace to profiles documentation is on this page: https://grafana.com/docs/pyroscope/latest/configure-client/trace-span-profiles/dotnet-span-profiles/

Tasks:
* Verify the information is correct
* Which config options are useful for this?
* Provide an example in the config option for the tracing integration