Scroll all the way to the bottom until you see "PKI CA Certificate Bundles: PKCS#7"
Click the download link that says "For DoD PKI Only - Version 5.0"
When the zip file is done downloading, open a terminal and go to that directory and unzip the file.
Now cd into the newly created directory.
Now run the following command to import the p7b files:
for n in *.p7b; do certutil -d sql:$HOME/.pki/nssdb -A -t TC -n $n -i $n; done
To check the status of the certs installed you can run:
certutil -d sql:$HOME/.pki/nssdb/ -L