ARROW-11821: [Rust] Edit Rust README

[pierwill]

Edits and fixes for some missing words, punctuation, and wording.

[github-actions]

Thanks for opening a pull request!

Could you open an issue for this pull request on JIRA?
https://issues.apache.org/jira/browse/ARROW

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

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

See also:

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

[alamb]

@pierwill thank you -- why did you close this PR?

[pierwill]

Ah! Hello, @alamb! Creating an account on a new service seemed like a lot for a simple docs PR. 🐑 😬

[alamb]

@pierwill I understand your position. Conveniently I have been working on a script to improve the experience (#9594) so I am going to reopen this PR and create the JIRA for it. It seems a shame to lose your work over a process issue

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11821

[alamb]

The integration test failures look like https://issues.apache.org/jira/browse/ARROW-11717 (since hopefully fixed)

[alamb]

Thanks @pierwill