Add brief contributor guidelines to docs/README.md and/or docs/contributing.md

[jhkrug]

Things like:

• We write for a world-wide, international, multilingual audience where English may not be the first language so clarity and simplicity are vital.
• Be aware of the SUSE and Microsoft style guides we use.
• Use simple language (for example, use and not leverage). Avoid English idioms implying background cultural understanding. An example: "Details have been glossed over". This is wonderful idiomatic English. But to fully understand it you have to understand that "gloss" is a type of shiny paint, the "over" refers to painting over and hiding or covering the details of some feature. All good stuff, none of which is relevant to understanding and using Epinio. So in this case use, perhaps, "Details are not included here".
• Use semantic linebreaks, that is, one sentence per line
• Pointer to a code of conduct for our projects

A few other things maybe, but short and sweet is best.