User-guide refresh (#99)

* Add hugo style blockquotes and infoblock styling for paragraphs

* Rearrange and rewrite parts of the userguide

* Correction re properties from review

Co-authored-by: Val Lorentz <vlorentz@softwareheritage.org>

* Second revision of userguide refresh

* Apply review contribution; better way to introduce keywords

Co-authored-by: Val Lorentz <vlorentz@softwareheritage.org>

* Proofread fix

* Retract the diagram, pending workshopped replacement

* Mention the use of  prefix for use of additional schema.org terms

* Use a real life example of schema: prefix use

* Better describe how the terms page indicates types

* Mention tools page in the userguide

* Remove stray char

* Changes for Context and Referencing sections

* Rearrange doc and add section describing people, roles, orgs etc.

* Apply suggestions from code review

Co-authored-by: Val Lorentz <vlorentz@softwareheritage.org>

* Improve explanation of  per feedback

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Co-authored-by: Val Lorentz <vlorentz@softwareheritage.org>

Author: meldra