add note to ExternalPackage doc
add note to ExternalPackage doc

Change-Id: I920e0f6cea18c825dc5786b6b4f2df1c0ddb890d

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core