Create 3.0-SDK.md (dotnet#14363)

Rick Anderson · web-flow · commit 4aebff5bce27 · 2019-09-17T14:03:17.000-07:00
diff --git a/aspnetcore/includes/3.0-SDK.md b/aspnetcore/includes/3.0-SDK.md
@@ -0,0 +1 @@
+[.NET Core 3.0 SDK RC1 or later](https://dotnet.microsoft.com/download/dotnet-core/3.0)

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	`1`	`+[.NET Core 3.0 SDK RC1 or later](https://dotnet.microsoft.com/download/dotnet-core/3.0)`