Add gnome-shell-extensions to the packages needed for Ubuntu (#1232)

* Add gnome-shell-extensions to the packages needed for Ubuntu

Ubuntu 24.04 doesn't ship with gnome-shell-extensions

* Update pop-shell.md

* improv: List reason for installing extension-prefs package

---------

Co-authored-by: Jacob Kauffmann <jacobgkau@users.noreply.github.com>
Co-authored-by: Aaron Honeycutt <aaron@system76.com>

content/pop-shell.md

@@ -15,10 +15,10 @@ tableOfContents: true
 
 #### For Ubuntu-Based Distros
 
-In order to build Pop Shell from source, we'll first need to install the build dependencies and <u>git</u> to clone the repository:
+In order to build Pop Shell from source, we'll first need to install the build dependencies, <u>git</u> to clone the repository, and the <u>Extensions</u> app to provide a GUI for enabling/disabling extensions and changing advanced extension settings:
 
 ```bash
-sudo apt install git node-typescript make
+sudo apt install git node-typescript make gnome-shell-extension-prefs
 ```
 
 **Note:** these instructions assume an Ubuntu-based distro; other distributions (see examples below) will use different package managers, and may have different package names.