[DEBUG][Vs2019] Adding a startvs.cmd would help

[tebeco]

Describe the bug

Can't debug from Visual Studio. As dotnet-try was designed during preview "times", multiple brreaking changes occured. A perfect example would be this one : https://devblogs.microsoft.com/aspnet/asp-net-core-and-blazor-updates-in-net-core-3-0-preview-9/

As this repository seems to be built for preview7, there was some breaking changes.

A file like startvs.cmd woud be helpfull in order to set variables like DOTNET_ROOT to the local dotnet install

Aspnetcore team example is here: I have no idea if it's supposed to be part of arcade or not to be honest

@ECHO OFF
SETLOCAL

:: This command launches a Visual Studio solution with environment variables required to use a local version of the .NET Core SDK.

:: This tells .NET Core to use the same dotnet.exe that build scripts use
SET DOTNET_ROOT=%~dp0.dotnet
SET DOTNET_ROOT(x86)=%~dp0.dotnet\x86

:: This tells .NET Core not to go looking for .NET Core in other places
SET DOTNET_MULTILEVEL_LOOKUP=0

:: Put our local dotnet.exe on PATH first so Visual Studio knows which one to use
SET PATH=%DOTNET_ROOT%;%PATH%

SET sln=%1

IF "%sln%"=="" (
    echo Error^: Expected argument ^<SLN_FILE^>
    echo Usage^: startvs.cmd ^<SLN_FILE^>

    exit /b 1
)

IF NOT EXIST "%DOTNET_ROOT%\dotnet.exe" (
    echo .NET Core has not yet been installed. Run `%~dp0restore.cmd` to install tools
    exit /b 1
)

start %sln%

[tebeco]

i'm attempting to actually make a PR with the file but it seems that it trigger other issues, i'll try to investigate latter, but you might go way faster than me on that i guess ^^