Users.md: add slapt-get

@jaos please review

docs/markdown/Users.md

@@ -145,6 +145,7 @@ format files
  - [scrcpy](https://github.com/Genymobile/scrcpy), a cross platform application that provides display and control of Android devices connected on USB or over TCP/IP
  - [Sequeler](https://github.com/Alecaddd/sequeler), a friendly SQL client for Linux, built with Vala and Gtk
  - [Siril](https://gitlab.com/free-astro/siril), an image processing software for amateur astronomy
+ - [slapt-get](https://github.com/jaos/slapt-get), an APT like system for Slackware package management
  - [Spot](https://github.com/xou816/spot), Rust based Spotify client for the GNOME desktop
  - [SSHFS](https://github.com/libfuse/sshfs), allows you to mount a remote filesystem using SFTP
  - [sway](https://github.com/swaywm/sway), i3-compatible Wayland compositor