docs: clarify behavior of deprecated withFirstRecordAsHeader()

Author: makarandhinge

src/main/java/org/apache/commons/csv/CSVFormat.java

@@ -2788,6 +2788,9 @@ public CSVFormat withEscape(final Character escape) {
      *                           .get();
      * </pre>
      *
+     * <p><b>Note:</b> Any previously set headers are reset to empty.
+     * The resulting format will have {@code skipHeaderRecord = true}.</p>
+     *
      * @return A new CSVFormat that is equal to this but using the first record as header.
      * @see Builder#setSkipHeaderRecord(boolean)
      * @see Builder#setHeader(String...)