add to guide: `component.author` & `component.manufacturer`

[jkowalleck]

update guide with the new features introduced by CycloneDX/specification#379

❗ this issue is only about component.author & component.manufacturer

• add component.manufacturer as "OrganizationalEntity"
  -- fixes #346
• add component.authors as list of "OrganizationalContact"
  -- fixes #335
• deprecate component.author in favour of component.authors and component.manufacturer
  • reason: value was described to be a string that could represent person(s) or organization(s).
    So let's introduce dedicated fields for both of these:
    Organizations are represented by the new @.manufacturer &
    persons are represented by the new @.authors.