fdo#85686 update help page for Calc Option Formula

Calc's Formula option page has a new entry related to large file recalculation

Change-Id: I9f4a5834ee58905d865aaedab25bd692445610d0
Reviewed-on: https://gerrit.libreoffice.org/12165
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>