ARROW-17512: [Doc] Updates to crossbow documentation for clarity

[lafiona]

Overview

While setting up a queue repository for testing changes to crossbow, we noticed some updates that can be made to help future developers set up their environment.

Implementation

1. Clarify Travis CI auto-cancellation default behavior.
2. Fix broken links referenced by instructions.
3. Minor typos.

Testing

1. Qualified by performing a directory level sphinx build and visually verifying the changes.

Notes

Thank you for your help on this pull request, @kevingurney!

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on JIRA? https://issues.apache.org/jira/browse/ARROW

Opening JIRAs ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename pull request title in the following format?

ARROW-${JIRA_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - How to contribute patches

[github-actions]

https://issues.apache.org/jira/browse/ARROW-17512

[github-actions]

⚠️ Ticket has not been started in JIRA, please click 'Start Progress'.

[pitrou]

LGTM in general. Just a couple comments.

[pitrou]

@lafiona @kevingurney Sorry, I noticed some other items that needed updating as well! (see the comments I posted above)

[pitrou]

+1, this is a nice improvement. Thank you @lafiona @kevingurney

[pitrou]

Will wait for CI before merging.

[ursabot]

Benchmark runs are scheduled for baseline = ec714db and contender = 60c9383. 60c9383 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
[Failed ⬇️0.78% ⬆️0.0%] test-mac-arm
[Failed ⬇️0.0% ⬆️0.0%] ursa-i9-9960x
[Finished ⬇️0.36% ⬆️0.04%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] 60c93833 ec2-t3-xlarge-us-east-2
[Failed] 60c93833 test-mac-arm
[Failed] 60c93833 ursa-i9-9960x
[Finished] 60c93833 ursa-thinkcentre-m75q
[Finished] ec714db3 ec2-t3-xlarge-us-east-2
[Finished] ec714db3 test-mac-arm
[Failed] ec714db3 ursa-i9-9960x
[Finished] ec714db3 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