Install new help files

Change-Id: I8fc26aadfa7509e19a6f4fb5941b6c1eb9cf9258
Reviewed-on: https://gerrit.libreoffice.org/6576
Tested-by: Andras Timar <andras.timar@collabora.com>
Reviewed-by: Andras Timar <andras.timar@collabora.com>