update readme to include all the env var's that are used to configure the server

[jasoncalabrese]

No description provided.

[jasoncalabrese]

good catch @jjmason

[bewest]

Here is preview link: https://github.com/nightscout/cgm-remote-monitor/blob/wip/readme-env-update/README.md

I added some links to the update-fork, mongostring, and configure tools.
I also created two tables with the things people might be interested in up front and center, clearly marked the one REQUIRED thing, and the rest of the optional things.

[jasoncalabrese]

nice, some of the env's are code other just CAPS
Core should probably be first too

[jasoncalabrese]

I'm going to update now

[bewest]

Looks ok, I think the labs/features table should be first, based on how often it's likely to be used.
The only one required environment variable is covered in detail in other places, so I'm guessing people are going to want the labs/features table most often.

[jasoncalabrese]

My thinking is that it would help someone get started it they saw the required/core vars first, but you have a good point too. Either way works for me.

[bewest]

Looks like the code fences make the thing do awful things with the scrollbars.

[coveralls]

Changes Unknown when pulling 874c48f on wip/readme-env-update into * on dev*.