[gimp-web] devel-docs: update the mirror-howto introduction with Mirrorbits info.

[Jehan <jehanp src gnome org>]

commit e336b25db699a4de764f4950902468ab69edde7a
Author: Jehan <jehan girinstud io>
Date:   Mon Aug 29 16:40:33 2022 +0200

    devel-docs: update the mirror-howto introduction with Mirrorbits info.

 devel-docs/mirror-howto.md | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/devel-docs/mirror-howto.md b/devel-docs/mirror-howto.md
index ba077ba7..3a722bc9 100644
--- a/devel-docs/mirror-howto.md
+++ b/devel-docs/mirror-howto.md
@@ -4,11 +4,15 @@
 
 Mirrors are synced from the static download server `download.gimp.org`
 (a.k.a. `master.gnome.org`).
-Current infrastructure is a basic round-robin rotation managed through
-[Apache rewrite
+Current infrastructure is using
+[Mirrorbits](https://github.com/etix/mirrorbits) which handles mirror
+geoIP-based redirection, health check (and removing down mirrors from
+rotation automatically), security checks and more for us.
+
+We have some redirection still available as [Apache rewrite
 
rules](https://gitlab.gnome.org/Infrastructure/puppet/-/blob/0df77787596314f41de55b270e016cfd99ce2a53/modules/httpd/files/sites.d/download.gimp.org.conf#L65-82)
-which will redirect `download.gimp.org/mirror/*` URLs to the same file
-at a random mirror from the list.
+so that old mirrored URIs (starting with `/mirror/`), from the time we
+had an Apache-based round-robin rotation, now just redirect to root.
 
 The list of mirrors in rotation is found at: `/etc/httpd/download.gimp.org.map`