[R] Update arrow.Rmd vignette

[asfimport]

A slight refresh of the table describing the R to Arrow and Arrow to R data type mapping

Reporter: Nicola Crane / @thisisnic
Assignee: Nicola Crane / @thisisnic

PRs and other links:

• GitHub Pull Request #11202

_{Note: This issue was originally created as ARROW-13397. Please see the migration documentation for further details.}

[asfimport]

Jonathan Keane / @jonkeane:
Issue resolved by pull request 11202
#11202