Redesing the codeowners documentation

[mszostok]

Description

Currently, most of the validator documentation is placed in main README.md file. This makes it hard to read and check which sections are described.

In this task documentation should be split to a dedicated .md files. The ToC in /docs folder should be updated.

Scratch: expose documentation using some static state generator, e.g.:

• Hugo
• mdbook
• Gatsbyjs

Reasons

It needs to be more readable to the user. Necessary information should be available in easy way.