ARROW-18238: [Docs][Python] Improve docs for S3FileSystem

[milesgranger]

Will fix ARROW-18238

[github-actions]

https://issues.apache.org/jira/browse/ARROW-18238

[pitrou]

@wjones127 Would you like to review this?

[jorisvandenbossche]

Thanks for the PR! I think we can expand the explanation a bit more, added a few suggestions

[jorisvandenbossche]

Thanks for the update!

[ursabot]

Benchmark runs are scheduled for baseline = 92c9f94 and contender = 94cf74f. 94cf74f is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Finished ⬇️0.27% ⬆️0.0%] test-mac-arm
[Finished ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.14% ⬆️0.0%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] 94cf74f3 ec2-t3-xlarge-us-east-2
[Finished] 94cf74f3 test-mac-arm
[Finished] 94cf74f3 ursa-i9-9960x
[Finished] 94cf74f3 ursa-thinkcentre-m75q
[Finished] 92c9f942 ec2-t3-xlarge-us-east-2
[Finished] 92c9f942 test-mac-arm
[Finished] 92c9f942 ursa-i9-9960x
[Finished] 92c9f942 ursa-thinkcentre-m75q
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java