Clarify which .editorconfig options are supported

[Documentation](https://github.com/dotnet/format/blob/main/docs/Supported-.editorconfig-options.md) says:

> The dotnet-format global tool supports the core set of [EditorConfig options](https://github.com/editorconfig/editorconfig/wiki/EditorConfig-Properties)* as well as the [.NET coding convention settings for EditorConfig](https://docs.microsoft.com/en-us/visualstudio/ide/editorconfig-code-style-settings-reference?view=vs-2019).

I tried setting `csharp_new_line_before_members_in_object_initializers = true` and it did nothing. Documentation [is here](https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/formatting-rules#csharp_new_line_before_members_in_object_initializers).

I tried to look into source code but found only whitespace, newline, usings, etc formatters. So does this tool support codestyle rules defined by microsoft? Or does it rely on analyzers installed from SDK/NuGet? (maybe i misunderstand some concepts here...)

Project targets `aspnetcore 2.2`
SDKs i have installed: `2.2, 3.1, 5.0`