Creating New Administrator Acount

So I am following the following post so I can create a new administrator account: https://tr.im/YGRfC

I enter the command rm /db/.AppleSetupDone

And the computer prompts me with the following: override -w---r-- /root/wheel /var/db/.AppleSetupDone? (It says something like that) I type in: yes and then it says “read only file system” after I reboot nothing happens, I don’t have to create a new account or do anything like that. I suspect it is because the file system is “read-only” is there anyway around that?