Howto mount drive as read-only with fstab
You simply have to add the ro mount option, which stands for "read-only".
In /etc/fstab entries, mount options are specified in the 4th column of each entry, so you could append it to that one e.g. like this:
/dev/disk/by-uuid/68271755-703c-48e6-a935-c1237de6b1a8 /mnt/HDD01 auto ro,nosuid,nodev,nofail,x-gvfs-show 0 0
More information can be found by typing man fstab and man mount.