Fix documentation for end_year option of date_helper [ci skip]

- While editing an existing record, end_year is equal to current selected year plus 5 by default.
- While editing an existing record, start_year is equal to current selected year value minus 5 by default.
- Fixes #13552

Acked-by: Prathamesh Sonpatki <csonpatki@gmail.com>

Acked-by: Prathamesh Sonpatki <csonpatki@gmail.com>
Merge pull request #13579 from prathamesh-sonpatki/issue-13552

Fix documentation for end_year option of date_helper [ci skip]
No need to use fixed size font [ci skip]