ShellPkg/UefiShellAcpiViewCommandLib: Change the note in uni

ShellPkg/UefiShellAcpiViewCommandLib: Change the note in uni

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1146

Add DSDT and SSDT description in the help information. Depend
on the implement of UefiShellAcpiViewCommandLib, the "acpiview"
command support to show all present type in the system not only
support the listed type in the help information. So change the
help information of this command.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>