docs: Prometheus client install instructions

[tgasser-nv]

Description

This PR adds the command to install prometheus-client so following steps in the tutorial work.

Related Issue(s)

VDR Issue 13

Checklist

• I've read the CONTRIBUTING guidelines.
• I've updated the documentation if applicable.
• I've added tests if applicable.
• @mentions of the person or team responsible for reviewing proposed changes.

[greptile-apps]

Greptile Summary

This PR adds prometheus-client as an explicit install dependency to the Prometheus scraping snippet and appends a short sentence explaining why it is required.

• The code example already imports start_http_server directly from prometheus_client (line 132), so declaring the package explicitly is correct and prevents a missing-import error for users who copy the snippet verbatim.
• Although opentelemetry-exporter-prometheus pulls in prometheus-client transitively, explicitly listing it aligns with the document's pattern of showing every required package in the install command.

Confidence Score: 5/5

Documentation-only change with no impact on runtime behavior; safe to merge.

The change is a single-line addition to an install command and a one-sentence clarification note. The added package (prometheus-client) is already used directly in the code example on line 132, so the documentation now accurately reflects what needs to be installed.

No files require special attention.

Important Files Changed

Filename	Overview
docs/observability/metrics/opentelemetry-integration.md	Adds prometheus-client to the Prometheus pip install command and a one-line note explaining it is needed for start_http_server; change is accurate and consistent with the code example on line 132.

Sequence Diagram

sequenceDiagram
    participant User
    participant prometheus_client
    participant PrometheusMetricReader
    participant MeterProvider
    participant Prometheus

    User->>prometheus_client: "start_http_server(port=9464)"
    Note over prometheus_client: Exposes /metrics HTTP endpoint
    User->>PrometheusMetricReader: PrometheusMetricReader()
    User->>MeterProvider: "MeterProvider(metric_readers=[reader])"
    Note over MeterProvider: IORails emits metrics through MeterProvider
    Prometheus->>prometheus_client: GET /metrics (scrape)
    prometheus_client-->>Prometheus: Prometheus exposition format

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between a6ab357 and 4aaad58.

📒 Files selected for processing (1)

• docs/observability/metrics/opentelemetry-integration.md

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📝 Walkthrough

Walkthrough

This PR updates the Prometheus scraping setup documentation by adding the prometheus-client dependency to the installation instructions and clarifying that this dependency is required because the example uses start_http_server to expose the scrape endpoint.

Changes

Prometheus Dependency Documentation

Layer / File(s)	Summary
Prometheus dependency documentation docs/observability/metrics/opentelemetry-integration.md	Installation command updated to include prometheus-client, with clarified note explaining it is required for the start_http_server scrape endpoint used in the example.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Suggested reviewers

• Pouyanpi
• cparisien
• miyoungc

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title 'docs: Prometheus client instructions' is directly related to the main change: updating Prometheus scraping installation instructions to include the prometheus-client dependency.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Test Results For Major Changes	✅ Passed	This PR contains minor documentation-only changes (+3/-1 lines) to the Prometheus installation instructions. The custom check permits passing minor changes without test results documentation.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/otel-prometheus

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

Documentation preview

https://nvidia-nemo.github.io/Guardrails/review/pr-1894