bug#34625: [PATCH] Documentation: Update `guix challenge` diffing

[Ludovic Courtès]

Hi!

mikadoZero <address@hidden> skribis:

>>From ea59d81de86fd5179eebf9782fbe66213ed59397 Mon Sep 17 00:00:00 2001
> From: mikadoZero <address@hidden>
> Date: Fri, 22 Feb 2019 18:24:20 -0500
> Subject: [PATCH] Documentation: Update `guix challenge` diffing.
>
> Add /gzip/ part into url which has the benefit of matching the output of
> `guix challenge`.  Change the commands to include gunzip in the pipeline as
> they are working on gzipped files.  Add reference to `guix challenge` in `guix
> archive` section where talking about challenging.

I changed the 2nd example to /lzip, adjusted the commit log to match our
conventions, and applied.

Thanks!

Ludo’.