[Development Guidelines] Add a official styleguide for Yoga2 in the docs

[guledali]

When you're working in a team, it's really good to have a common practice. What's is the best practices/patterns for Yoga2 or GraphQL Nexus for that matter, everything in programming have dos and donts

Having a styleguide similar to https://vuejs.org/v2/style-guide/ or https://learn-vuejs.github.io/vue-patterns/patterns/ will make on boarding easier and more appealing for large teams as well.

One example would be looking at Gitlab GraphQL API Styleguide