Take things out of "Getting Started" that aren't actually about Getting Started #213

I've already moved some of these... but I think that this section should be reserved for the few things one would need to do to make a first API request and to start trying out other popular endpoints. I'd say these should be:

• Introduction
• About
• Access and authentication
• Client libraries
• Your first API request

The "Your first API request" guide duplicates some of what's in "Introduction", but I've figured we should keep things as is until we write a fuller getting-started guide/tutorial.

I would have made another section for the other items by now, but I don't know what to call it 🫠