Fix s3 readme with refined metrics

[plyfager]

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Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

Who can help? @ them here!

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.81%. Comparing base (d1039e0) to head (4b43138).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #484   +/-   ##
=======================================
  Coverage   74.81%   74.81%           
=======================================
  Files         145      145           
  Lines       11015    11015           
  Branches     2097     2097           
=======================================
  Hits         8241     8241           
  Misses       2233     2233           
  Partials      541      541           

Flag	Coverage Δ
unittests	74.81% <ø> (ø)

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