Add "style guide" to docs

[FloEdelmann]

What problem does this feature solve?

It would be helpful to have a style guide, similar to Vue's (https://vuejs.org/v2/style-guide/), so that arbitrary choice in Nuxt.js apps is further reduced. Those guidelines could be enforced with a linter, like ESLint or its Vue Plugin.

In particular, a "Component options order" rule came to my mind (similar to https://vuejs.org/v2/style-guide/#Component-instance-options-order-recommended). I've already opened a PR (#1107) to eslint-plugin-vue. Please comment there on the suggested order.

[Atinux]

Closing since the PR is merged, thank you @FloEdelmann