Soda Core docs TODO - Run your first scan

[janet-can]

• change title to Run a scan. The "first" only applies to the first time you use it and this is reference material that you might return to a few times in order to remember the scan command. Also, "first" competes with Get started which is just a tiny friction that we can reduce by pointing clearly to One Starting Point.
  ...Aha! I see at the end, "Next, scan your own data" that this was meant to be the tutorial. Let's make the tutorial a separate, beautiful, short, end-to-end experience with demo data and call it Quick Start. Then we can use this page for details about what a scan does, the input, output, etc. Reference Scans, though obviously with all references to cloud removed.
• edit for complete sentences and grammar
• remove demo DB bit in favour of putting the whole example/get started/tutorial in the Quick Start page
• separate configuration file and checks files into separate pages. Explain files more thoroughly; reference Soda SQL warehouse YAML and scan YAML
• replace instances of SodaCL file with checks.yaml
• move this page in the TOC to fifth place: Get started > Install > Configuration YAML > Checks YAML > Run a scan
• include all the content in the Soda Core scan reference page, cleaned up and explained.