docs: add benchmark speed for r2

[bhimrazy]

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Add benchmark speed for r2

Speed to stream Imagenet 1.2M from other cloud storage providers:

Storage Provider	Framework	Images / sec 1st Epoch (float32)	Images / sec 2nd Epoch (float32)
Cloudflare R2	LitData	5335	5630

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in GitHub issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79%. Comparing base (0635369) to head (1202d4a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #551   +/-   ##
===================================
  Coverage    79%    79%           
===================================
  Files        40     40           
  Lines      6081   6081           
===================================
  Hits       4803   4803           
  Misses     1278   1278           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.