Contributor-facing documentation updates

[Bankso]

Ideas for docs updates:

• CCKP docs:
  • Add a screenshot on “Navigating the DSP” with key elements circled and explained with a number key (like other things in the CCKP docs were previously)
  • Model visualization - facilitated by RDF encoding of data models

-Data model docs:

• Add links to data model docs for basic metadata templates, if they aren’t in there already
• Model visualization - facilitated by RDF encoding of data models
• Add content for assay-specific metadata models