docs: fs example

packages/csv/samples/.gitignore

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+example.fs.input.csv
+example.fs.output.csv

packages/csv/samples/example.fs.js

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+import fs from "node:fs";
+import assert from "node:assert";
+import { finished } from "node:stream/promises";
+import { parse, transform, stringify } from "csv";
+
+const __dirname = new URL(".", import.meta.url).pathname;
+await fs.promises.writeFile(
+  `${__dirname}/example.fs.input.csv`,
+  "a,b,c\n1,2,3"
+);
+
+await finished(
+  fs
+    .createReadStream(`${__dirname}/example.fs.input.csv`)
+    .pipe(parse())
+    .pipe(transform((record) => record.reverse()))
+    .pipe(stringify())
+    .pipe(fs.createWriteStream(`${__dirname}/example.fs.output.csv`))
+);
+
+assert.equal(
+  await fs.promises.readFile(`${__dirname}/example.fs.output.csv`, "utf8"),
+  "c,b,a\n3,2,1\n"
+);