docs: adds verify ID Token IAP to samples table of contents

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Commits in this repo since last synth:
c532b14 chore(deps): update dependency linkinator to v2 (#886)
a98e386 feat: support for verifying ES256 and retrieving IAP public keys (#887)
e671629 build: add GitHub actions config for unit tests (#888)
163e43d test: modernize mocha config (#884)
58e5029 chore: skip img.shields.io in docs test
13e8cfb chore(deps): update dependency @types/mocha to v7
634cf6a chore: release 5.9.2 (#882)
63c4637 fix: populate credentials.refresh_token if provided (#881)

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synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
On branch autosynth
nothing to commit, working tree clean
HEAD detached at FETCH_HEAD
nothing to commit, working tree clean
.eslintignore
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.github/ISSUE_TEMPLATE/bug_report.md
.github/ISSUE_TEMPLATE/feature_request.md
.github/ISSUE_TEMPLATE/support_request.md
.github/PULL_REQUEST_TEMPLATE.md
.github/release-please.yml
.github/workflows/ci.yaml
.jsdoc.js
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.kokoro/publish.sh
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.nycrc
.prettierignore
.prettierrc
CODE_OF_CONDUCT.md
CONTRIBUTING.md
LICENSE
README.md
codecov.yaml
renovate.json
samples/README.md
synthtool > Wrote metadata to synth.metadata.