Further enhance documentation.

[MaxDall]

The current documentation and guidelines lacks crucial information and should be expanded with the following:

how_to_contribute.md

• A best practice for contributing a parser (First add to publisher collection -> validation -> ...)
• A simple rule on how to choose where to use the information from (meta vs ld vs layout)
• A explain of the functionality of BaseParser.parse() and it's correlation with Precomputed (should be done after More descriptive naming schema for Precomputed #94)
• Remove @function from documentation since it isn't is use yet.

attribute_guidelines.md

• Add commonly used extraction patterns to attributes. i.e:

self.precomputed.ld.bf_search("datePublished")

code documentation

• Add precise documentation to src/parser/html_parser/utils.py
• Change parameter naming schema

[dobbersc]

Added to the first point: Also some common patterns for the attributes fields. E.g. keywords and topics for the topics attribute.