Building spacecraft is an exceedingly difficult task. Every gram of extra weight makes it harder and more expensive to launch your ship. So nothing is included on spaceships unless absolutely necessary. (At this point someone is going to point out the record attached to the Voyagers: this was necessary for PR purposes. :-)
Anyhow, it is exceedingly unlikely that we or any alien species is every going to see either of the Voyagers again, so building any docking facility would have added weight for no good reason.
The word "docking" implies access to the interior of the satellite, as in docking with the ISS. However there is no "inside" of Voyager, or indeed most unmanned spacecraft, as it's packed solid with kit. However if you use the word in the broader sense you could argue that the Hubble telescope has docking facilities so astronauts can service it.