Improve note about specifying time ranges for ICON data

[schlunma]

Link to documentation: https://esmvaltool--3217.org.readthedocs.build/projects/ESMValCore/en/3217/quickstart/find_data.html#icon

---

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.48%. Comparing base (90cf5ad) to head (93cb1d2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3217      +/-   ##
==========================================
- Coverage   96.50%   96.48%   -0.02%     
==========================================
  Files         282      282              
  Lines       16407    16407              
==========================================
- Hits        15833    15830       -3     
- Misses        574      577       +3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.