Direct people to the maintained fork of this library

[FeldrinH]

Continuation of #1016.

It appears that this library is unmaintained and will remain unmaintained for the foreseeable future. However, there is a maintained fork of this library at https://github.com/gopacket/gopacket. Would it be possible to add a note to the readme or some other more visible place that would redirect people to that fork? Currently this repo comes up first in many search engines, which initially made me miss the more maintained fork and I suspect that I am not the only one. The fact that a lot of new issues are still filed in this repo indicates that many people don't know that there is a new, more maintained fork.

[lhausermann]

It will be better. @gconnell, is it okay for you to be the originator of Gopacket? It would probably mean updating the README and moving the project as archived.