Create a guide to issue submissions

[thomasdavis]

When rejecting issues that have seemingly being debated before, it would be also good to point to a guideline-ish reason as to why.

Much like how Hacker News has their succinct points for moderation -> https://news.ycombinator.com/newsguidelines.html

A basic example would be, if only a small fraction of the world would use a new property (bad example: favorite_zoo), then it likely won't make it into this schematic. There are other projects which try to include all possibilities such as https://schemas.liquid-technologies.com/HR-XML/2007-04-15/