Clarify relationship with macpaw.com/the-unarchiver

We note
```
$ man unar | tail -n 1
The Unarchiver ...
$ unar --version
v1.10...
```
But then we also note
```
$ w3m -dump https://macpaw.com/the-unarchiver | grep Version
Latest Version: 4.3.6 (20 Oct 2023)
```

So please mention the relationship between the two "branches"(?)