Landing page improvements

[noahfalk]

https://docs.microsoft.com/dotnet/core/diagnostics

1. Our landing page mentions debuggers, but omits profilers. We should add them.
2. Symbols and Unit Testing seem unnecessary as topics here.
3. 'Collect diagnostics in containers' perhaps should be in the tutorial list rather than the tool list?
4. Writing a custom diagnostic tool feels like a rare case and should be at the bottom of the page
5. We might want to put shortcuts or text at the top of the page so that it is obvious the tutorials are below.
6. The title only talks about tools. We should pick something more general purpose so it includes tutorials.