[R] Update python.Rmd vignette

[asfimport]

Proposed changes:

• Add link to where reader can learn about the different Arrow object types (the "internals" section of the "arrow" vignette) e.g. by calling vignette("arrow", package = "arrow")
• "we" -> "you"
• Brief description of what a virtualenv is
• "The package" -> which package?
• Update example objects to have different names
• Add reasons why you might want to use pyarrow to a brief list at start of vignette
• Move sentence starting with "Send isn't the right word" to own subsection on how this works

Reporter: Nicola Crane / @thisisnic
Assignee: Alenka Frim / @AlenkaF

PRs and other links:

• GitHub Pull Request #11914

_{Note: This issue was originally created as ARROW-13401. Please see the migration documentation for further details.}

[asfimport]

Nicola Crane / @thisisnic:
Issue resolved by pull request 11914
#11914