fdo#80481: Update Start Center help page.

Update Start Center help page with new features.

Change-Id: I052e0245a6e3598b561b6aaf43913be2a6387fca
Reviewed-on: https://gerrit.libreoffice.org/12159
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>