Added a readme file to the NuGet packages

[Guiorgy]

With the Visual Studio 17.13 update the NuGet package manager/browser shows a preview of the included readme.

Might want to consider embedding a readme with the packages moving forward, otherwise Visual Studio shows the following:

Ideally, each package would have a dedicated readme, but that would probably be too annoying to maintain, so for now I included the same file in every package.

I included the readme.source.md file, though if you'd prefer readme.md instead, I can change that.

[Guiorgy]

@dotnet-policy-service agree

[SimonCropp]

doesnt this make it difficult NuGet/NuGetGallery#8644 ?

[SimonCropp]

also Mermaid diagrams are not supported NuGet/NuGetGallery#8942

[Guiorgy]

Good point

[SimonCropp]

so whats the way forward?

[Guiorgy]

There are several options:

• Keep things as they were (EDIT: In other words close the PR)
• Embed one of the readmes as they are ignoring the problems
• Make a smaller simplified readme for embedding into the NuGet packages

Your choice really.

[SimonCropp]

Make a smaller simplified readme for embedding into the NuGet packages

happy to consider a PR that does this