Create a docs style guide

[oubiwann]

This can just start with a sample of all the different things that are styled:

• terminal code
• terminal code with emphasis
• source code
• code in a paragraph
• tables
• alert boxes
• warning boxes
• numbered steps/instructions
• various LFE logos (small grey, small black, small color, large color, etc.)

It would just be a single page showcasing these things (and more), as a reminder to docs maintainers regarding the available styles and the prescribed way to do things.

Part of epic #96

[oubiwann]

Done ages ago.