Explaining graph visualization, partially resolves #275

[ianmilligan1]

GitHub issue(s):

If you are responding to an issue, please mention their numbers below.

• Clarification around network diagrams #275

What does this Pull Request do?

This pull request partially resolves #275 by explaining the graph visualization, both the in-browser sigma one as well as the Gephi download.

• Adds tooltip to collection page
• Refines documentation

How should this be tested?

It should build locally, pass style checks (I've tried my best), and the tooltip should pop up.

[codecov-io]

Codecov Report

Merging #277 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #277   +/-   ##
=======================================
  Coverage   96.22%   96.22%           
=======================================
  Files          35       35           
  Lines         557      557           
=======================================
  Hits          536      536           
  Misses         21       21

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