`dotnet` spelling

[nohwnd]

As far as I can see. This guideline does not mention when it is appropriate to use dotnet, and what is the correct capitalization. E.g. if dotNet is permissible. It would be nice to get clarity on that, since it is used in the name of this repository, as the name of the CLI tool, and throughout the guide as well.

[mairaw]

Something for us to discuss @Mehul and @kkbrooks when reviewing the brand guidelines, even though it would be more of a footnote than actual guidelines IMO. When referring to a tool name or repo name, you're not really talking about the .NET brand.

For now, I'd just use all lowercase like we do on docs, etc.
e.g. https://learn.microsoft.com/en-us/dotnet/core/tools/dotnet-vstest