Add clarification about interim state of repo consolidation (#13015)

Author: nguerrera

README.md

@@ -1,6 +1,10 @@
 # This Repo has moved!
 
-Going forward, this repo will be merged into https://github.com/dotnet/sdk.  Previous releases will still be serviced out of this repo.
+Going forward, this repo will be merged into https://github.com/dotnet/sdk.  Previous releases (prior to .NET 5) will still be serviced out of this repo.
+
+At this point in time, the source code has been merged into https://github.com/dotnet/toolset, which will shortly itself be merged into https://github.com/dotnet/sdk.
+
+If you have an issue to file, log it at https://github.com/dotnet/sdk as that will be the final resting place. If you have a code change to code that used to be in this repo, you can submit a PR to https://github.com/dotnet/toolset, but keep in mind that the code will be moved shortly to https://github.com/dotnet/sdk. If your change is not urgent, then you may wish to wait for that to happen and submit to https://github.com/dotnet/sdk after the final consolidation there, in order to avoid having to migrate your changes to a new PR.
 
 For more information, see [dotnet/announcements#119 "Consolidating .NET GitHub repos"](https://github.com/dotnet/announcements/issues/119)
 
@@ -12,4 +16,4 @@ If you are looking for the latest nightly of the .NET Core SDK, see https://gith
 
 |Windows x64|
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-|[![Build Status](https://dev.azure.com/dnceng/internal/_apis/build/status/224)](https://dev.azure.com/dnceng/internal/_build?definitionId=224)|
+|[![Build Status](https://dev.azure.com/dnceng/internal/_apis/build/status/224)](https://dev.azure.com/dnceng/internal/_build?definitionId=224)|