Define or reference standards how to perform code reviews and document the process

[thomaskrause]

This could be a result of the literature review suggested in #10

• research existing standards
• link to these standards in the documentation, or describe how we apply a compiled set of standards, in the project docs.

[sdruskat]

This is for the project documentation.
The actual review process and involved technology should still be included in the maintenance docs.

[sdruskat]

Split part regarding maintainer docs to hexatomic/hexatomic#32.

[sdruskat]

Changed original comment #13 (comment): Deleted last bullet as this is now hexatomic/hexatomic#32.