Should CONTRIBUTING.md be updated to list .NET 8

[dellch]

Just found this repo/tool and was browsing around.

It looks like the csproj files reference .NET 8, is that true? Should CONTRIBUTING.md be updated for this?

I can make the PR, but wanted to check first. The lines in CONTRIBUTING.md:

Get .NET 6

Grate is built with .NET 6, which just shipped in early November 2021. You can get it here and start building right away.