Add HDD Price Index to Datasets

[AdamDudley]

Summary

Adds the HDD Price Index open dataset to the Data Sets section, placed near the existing economic/financial dataset entries (FinancialData.Net, etc.).

• [HDD Price Index](https://github.com/AdamDudley/hddhunt-price-index) — Daily open dataset of the cheapest new internal 3.5" SATA hard-drive price per terabyte (USD/TB) by capacity tier on Amazon US, with a historical time series. Root-level CSV, JSON and JSONL; no login/auth required.
• Entry format matches the section style [Name](URL) - description, one sentence, no marketing language, https:// source link, placed next to similar datasets.

Tip Requirement (Required)

• Fully open source: $1 one-time tip.

The dataset is fully open source (public GitHub repository, CC BY 4.0, no paid tier or closed service).

Tip link acknowledged: https://github.com/sponsors/hmert

License Type (Required)

• Creative Commons (CC-BY, CC-BY-SA, etc.)

License details: CC BY 4.0 (data), MIT (accompanying refresh script). Declared in the repository LICENSE and README.md.

Your Relationship to This Project (Required)

• Owner

I author and maintain the dataset; submitting under my own GitHub identity.

Checklist

• I confirm the information above is accurate.
• I have read CONTRIBUTING.md and followed the repository format (single bullet in the most relevant section, existing style, https link, no marketing language, placed near similar entries).
• I verified links and descriptions in my change.

[hmert]

@AdamDudley hi, could you follow https://github.com/academic/awesome-datascience/blob/live/.github/pull_request_template.md

[AdamDudley]

Thanks @hmert — I've completed the PR template in the description above: Summary, License (CC BY 4.0), relationship (Owner), and the checklist. The resource is fully open source (public repo, CC BY 4.0, no paid tier). The entry is a single bullet in the Data Sets section following the existing [Name](URL) - description style. Happy to adjust wording or placement if you'd like anything changed.