Help page for Fill random numbers for new dialog

for new dialog layout.
See ac5e002e941dadc274e97b4c3afc009b6e5adbd4

Change-Id: I2f371a2ac2960c5905845761370b7e99a0a1d3ed
Reviewed-on: https://gerrit.libreoffice.org/11207
Reviewed-by: Olivier Hallot <olivier.hallot@edx.srv.br>
Tested-by: Olivier Hallot <olivier.hallot@edx.srv.br>