Meta docs need updated structure

[jharrell]

The "meta" docs, hosted under /about, have a few layers of nesting and don't quite make sense.

• https://www.prisma.io/docs/about/prisma-docs has content and acts as an index
• https://www.prisma.io/docs/about has no content and is an index
• https://www.prisma.io/docs/about/prisma-docs/about-the-docs has content, isn't an index

We should go through and clean up this section in addition to updating its content.