Added preview1/rc2 images for .NET Core and CLI Tools.

[MichaelSimons]

These images are available under a test Docker Hub repository if you want to pull them.

@naamunds, @dleeapho @glennc

[glennc]

This still requires @blackdwarf to add text and such to the .md right?

[MichaelSimons]

@glennc correct the readme content is just a placeholder until @blackdwarf provides the official content. My apologies for not calling this out.

[dleeapho]

Should we be thinking of onbuild based off of :core instead? With ENTRYPOINT ["dotnet"] users would build in their publish output folder and run their (portable) app with docker run microsoft/dotnet:onbuild myapp.dll it's more lightweight and I'm not sure whether the typical onbuild scenario needs the full sdk.

[MichaelSimons]

@dleeapho I am not sure I am following? onbuild as defined has to have the full sdk in order to restore and build. Where/when do you see this happening?

[dleeapho]

I positing that there is another scenario for onbuild, instead of restoring and building in-container that onbuild could also be used to quickly run any portable app. The onbuild would copy the dotnet publish directory contents and myapp.dll would be the args to the dotnet (muxer) entrypoint. In any case we can wait and see if there is a need for what I'm proposing.