Update the fields that allows any value to mention that " /prefix" is an exception that is not allowed

[Kb-Tay]

Currently, for example, our UG states that for address allows any value. However, giving the value " a/" for address will give an error of duplicate prefix. Update UG to be clearer that it does not allow prefix in value

[sopa301]

I think removing "/" would be easier to write

Edit: Nevermind, just mention it in the section before the commands