README.md: (misc) Fix example

Xlsx::worksheet_range() returns Result<T, E> not Option<Result<T, E>>

README.md

@@ -96,7 +96,7 @@ function.
 use calamine::{Reader, Xlsx, open_workbook};
 
 let mut excel: Xlsx<_> = open_workbook("file.xlsx").unwrap();
-if let Some(Ok(r)) = excel.worksheet_range("Sheet1") {
+if let Ok(r) = excel.worksheet_range("Sheet1") {
     for row in r.rows() {
         println!("row={:?}, row[0]={:?}", row, row[0]);
     }