Improves documentation for `csv_to_parquet()` for txt files

[ddotta]

Closes #11

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (961f0b0) 99.72% compared to head (02c1ef9) 99.72%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #48 +/- ## ======================================= Coverage 99.72% 99.72% ======================================= Files 16 16 Lines 361 361 ======================================= Hits 360 360 Misses 1 1 ``` | [Impacted Files](https://app.codecov.io/gh/ddotta/parquetize/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Damien+Dotta) | Coverage Δ | | |---|---|---| | [R/csv\_to\_parquet.R](https://app.codecov.io/gh/ddotta/parquetize/pull/48?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Damien+Dotta#diff-Ui9jc3ZfdG9fcGFycXVldC5S) | `100.00% <ø> (ø)` | |

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