chore(docs): refresh README cleanup savings estimates

[justinthelaw]

Motivation

• Refresh the per-component disk-savings guidance in README.md to reflect the most-recent passing CI matrix results and give users more realistic, directional estimates.
• Surface a short note clarifying that these numbers are approximate and may change as the hosted runner image is updated.

Description

• Updated the ## Inputs reference table with revised estimated disk-savings ranges for every remove-* option (for example remove-android, remove-cached-tools, remove-dotnet, etc.).
• Added an explicit estimated size for remove-powershell and adjusted several other ranges to better match recent CI observations.
• Inserted a short explanatory note above the inputs table stating that estimates are based on the latest passing CI matrix runs and are directional.
• Minor formatting adjustments to keep the inputs table aligned and readable.

Testing

• Queried the GitHub Actions API with curl and jq to list recent test.yml workflow runs and confirmed the latest completed run (22919453451) and its matrix jobs reported success for removal-specific test jobs.
• Fetched the job list for the run via curl '.../actions/runs/22919453451/jobs?per_page=100' | jq and validated each removal job name and conclusion: success.
• Inspected the check-runs for the commit via GitHub API and confirmed the relevant check run (test (remove-dotnet) and other matrix checks) returned conclusion: success.
• Ran git diff --check to ensure no formatting issues were introduced and the repository passed the local pre-commit/style checks (no errors reported).

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Codex Task