Clarify use of C# extension without C# Dev Kit

In addition to the clarification of the dependency direction mentioned in https://github.com/dotnet/vscode-csharp/issues/6171 I would really appreciate if the description of the C# extension includes even more instructions.

> While it is possible to use the C# extension as a standalone extension, we highly recommend using [C# Dev Kit](https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csdevkit).
> 1. Installing [C# Dev Kit](https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csdevkit) will automatically install this extension as a required dependency.
> 2. ...
> 3. ...

Please add another list of 1./2./3. instructions how to use this extension **without** C# Dev Kit!

I assume (but I am not sure) it would use OmniSharp instead, just like version 1 of the extension.