add AnnotationSeries example to docs

[stephprince]

Motivation

We are aiming for 100% coverage of all Neurodata types in our documentation. There is no example demonstrating the use of AnnotationSeries in the docs.

How to test the behavior?

cd docs
make clean && make html

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running ruff check . && codespell from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.92%. Comparing base (9de4d4c) to head (b1c2b0d).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1989   +/-   ##
=======================================
  Coverage   91.92%   91.92%           
=======================================
  Files          27       27           
  Lines        2713     2713           
  Branches      708      708           
=======================================
  Hits         2494     2494           
  Misses        145      145           
  Partials       74       74           

Flag	Coverage Δ
integration	72.87% <ø> (ø)
unit	82.89% <ø> (ø)

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[stephprince]

@bendichter I looked at some of the datasets using AnnotationSeries on DANDI and it seemed primarily associated with stimulus presentation, but let me know if you had a better example in mind.

[bendichter]

Looks great!