Commit log for reverts

[Ludovic Courtès]

Hola!

address@hidden skribis:

> commit a06a4f918243dc784f9089d60690559b72a4e308
> Author: Brett Gilio <address@hidden>
> Date:   Fri Jan 3 20:15:44 2020 -0600
>
>     Revert "gnu: Add swi-prolog."
>     
>     This reverts commit 3f37f3909712eb7269b6e8184c0d61bfc61b67f9.

When reverting changes, I think we should always add a sentence possibly
with a link explaining the revert, to make it easier to those of us
reading guix-commits and to our future selves looking at the commit log
and wondering what was going on back then.  :-)

Thoughts?

(Anyhow, I’m glad SWI-Prolog eventually made it!)

Thanks,
Ludo’.