Add first draft of 'quick reference' and 'explanation' docs

[jfy133]

Feel free to modify/re-write/extend/delete as you prefer!

[codecov-commenter]

Codecov Report

Base: 91.81% // Head: 91.81% // No change to project coverage :thumbsup:

Coverage data is based on head (a59170b) compared to base (cf7eae7). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #41 +/- ## ======================================= Coverage 91.81% 91.81% ======================================= Files 101 101 Lines 1392 1392 Branches 88 88 ======================================= Hits 1278 1278 Misses 92 92 Partials 22 22 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[Midnighter]

Cheers, thank you for those suggestions. I've switched the when & how.