Mark parts of style guide that are required and ones that are best practices

[dragonee]

Some parts will be enforced by us in every project (spacing, code block styles, etc.), some are best practices. It would help to mark them in some way as required rules and best practices. Symbols are to be defined.

For example - we could use an asterisk to define required rule.

Also there's an idea to sort them so that the required rules will generally be on top of the file, and best practices on bottom.