You must add the following RSP_ID and RSP_KEY properties to your msiexec command:

msiexec /i LDB-lab-v21501-you-must-read-readme.msi /qn RSP_ID=175754166 RSP_KEY=a93a7d81095c9889a859941298806b59

For Canvas Classic and Blackboard Original exams where students must launch LockDown Browser manually:

To create a desktop shortcut, add RSP_NAME with the shortcut text in quotes, for example: 
RSP_NAME="UZ Springfield"

To create a second shortcut if students also take exams at another institution, add RSP_ID2 and RSP_NAME2 where the ID is the Institution ID used in download links:
RSP_ID2="555444333" RSP_NAME2="UZ Shelbyville" 