suggest changing key server, because other caused error for gpg on some OSes

tl;dr: when using the keys.openpgp.org on alpine it seems like it fails to import completely, but keys.gnupug.net works flawlessly.

So, I have a project that builds kali every week and gives me an updated image weekly (more info here), but I verify the checksum every week. So, I definitely enjoyed hearing about in the most recent blog that this section was updated in the docs.

So, I updated my process to use the keyserver (like mentioned in the docs), and the pipeline failed when attempting to do it (ignore the shfmt error, but here is the failed build).

So, I tested it locally and sure enough it failed for me locally as well.

I tested it on ubuntu as well though, and it didn't fail on ubuntu...

So, I looked around a bit and saw that in the man docs it references using keys.gnupg.net, so I plugged that one in instead and everything worked. (modification here & successful CI run here).

I imagine that the docs would want to work no matter what distro you are on, so that is why I wanted to create this quick PR to point to the keyserver that I had used.

Let me know if there is anything else I need to do, and thank you for such an awesome project! ❤