[R] Add recipe on converting data from one format to another (e.g. CSV to Parquet)

(Show how can do open_dataset(..., as_data_frame = FALSE) followed by write_dataset(...) for efficiency and explain why it's efficient.

Start by locating the existing R recipe documentation and the open_dataset(..., as_data_frame = FALSE) and write_dataset(...) entry points. Add a recipe demonstrating conversion such as CSV to Parquet, and explain why this approach is efficient; the documentation is done when both the example and its efficiency rationale are clear.

Written by the indexing model from the issue text.