DOC: Add tutorials, porcupine to users TOC

[effigies]

Closes #2335.

[effigies]

Quickstart (already present): https://3869-791477-gh.circle-artifacts.com/0/home/circleci/work/docs/quickstart.html

User guide (added in this PR): https://3869-791477-gh.circle-artifacts.com/0/home/circleci/work/docs/users/index.html

[codecov-io]

Codecov Report

Merging #2503 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2503   +/-   ##
=======================================
  Coverage   66.87%   66.87%           
=======================================
  Files         327      327           
  Lines       42448    42448           
  Branches     5266     5266           
=======================================
  Hits        28387    28387           
  Misses      13362    13362           
  Partials      699      699

Flag	Coverage Δ
#smoketests	50.83% <ø> (ø)	⬆️
#unittests	64.22% <ø> (+0.04%)	⬆️

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[djarecka]

lgtm

[effigies]

Latest update also includes it in the user TOC on documentation.html.

Will merge on passing tests unless someone objects.