You cannot make the field readonly.
I do not have any examples, there are 2 ways that you can do this.
The first is to use custom CSS in the admin to hide the edit and delete action button for the field.
[data-key="YOU FIELD KEY"] .acf-input .link-wrap a {
display: none;
}
The second would be to add custom JavaScript to the admin to remove the action buttons instead of hiding them.
