Soda Core docs TODO - Soda Core Documentation/Overview

[Janet R]

• edit for complete sentences and grammar
• make all lists parallel (same tense, imperative, and same phrasing)
• remove features not available at release (will metric store be available?)
• expand How it works into a new sub-page with extensive detail; reference Soda SQL How it works
• explain SodaCL a bit. It's instrumental to Soda Core usage and deserves some illumination.
• briefly explain each code snippet example, like one sentence, in case a reader is newly entering data monitoring territory
• remove "Coming soon" as docs doesn't promise future releases. Things change, plans pivot-- let's not set expectations we cannot ruthlessly adhere to. Instead, let's have a section of "Data sources under consideration" and maybe an invitation to Contributors to build it.
• Change "Next, install it on your own..." to something more like a pointer to Quick start tutorial.