[wiki] [sites] Add farbfeld slackware package || Laslo Hunhold

[git]

commit 33b344bbf6b73a1d69ed4a097f2af2790c75ac91
Author: Laslo Hunhold <d...@frign.de>
Date:   Sun Feb 19 22:05:01 2023 +0100

    Add farbfeld slackware package
    
    Signed-off-by: Laslo Hunhold <d...@frign.de>

diff --git a/tools.suckless.org/farbfeld/index.md 
b/tools.suckless.org/farbfeld/index.md
index 341bb344..ed79e477 100644
--- a/tools.suckless.org/farbfeld/index.md
+++ b/tools.suckless.org/farbfeld/index.md
@@ -46,7 +46,8 @@ provide packages:
 * [FreeBSD](https://svnweb.freebsd.org/ports/head/graphics/farbfeld/)
 * [Gentoo](https://packages.gentoo.org/packages/media-gfx/farbfeld)
 * 
[NixOS](https://github.com/NixOS/nixpkgs/tree/master/pkgs/development/libraries/farbfeld)
-* [OpenBSD](http://ports.su/graphics/farbfeld)
+* [OpenBSD](https://ports.su/graphics/farbfeld)
+* [Slackware](https://slackbuilds.org/repository/15.0/graphics/farbfeld/)
 * [Ubuntu](https://packages.ubuntu.com/farbfeld)
 * [Void 
Linux](https://github.com/void-linux/void-packages/tree/master/srcpkgs/farbfeld)