Deprecation warning

[pieter-venter]

I think it is sensible to add clear deprecation warnings or a note of some kind in this repo. For example, the NuGet package for Microsoft.Diagnostics.Tracing.EventSource has not been updated since 2015.

Unfortunately, articles still link to this repo and if you Google for EventSource you will inevitably end up here, adding to the already confusing world of EventSource, EventPipes, ETW.