Explains what "for local development means"

[davidfowl]

When we say aspire is optimized for local development, we say it without explaining how it relates to the different things that make up aspire. One common point of confusion is that the aspire components are nuget packages used by your application, so are service defaults. Are those only for dev? They aren't but the overall message about "being optimized for dev" muddies the message.

We should explain (maybe via diagrams) how the various parts of the stack work in local dev and when deploying.

This should be in the overview.