[Python] Add compute module docs

[asfimport]

Reporter: Andrew Wieteska / @arw2019
Assignee: Andrew Wieteska / @arw2019

PRs and other links:

• GitHub Pull Request #8145

_{Note: This issue was originally created as ARROW-9967. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 8145
#8145