This change adds a few things to the .NET landing page:
- Add the .NET Core logo.
- A bit more about "why you might care."
- Add a basic code snippet.
- Add a Getting Started section. We want to drive people here
when first landing on this page as much as possible, since it's
the best experience (despite it being C#-only).
- Use the language switcher for C#/F#/VB templates.
- Reorder some content so most relevant is above the fold.
- Add CI/CD coverage of Azure DevOps pipelines and GitHub Actions.
