Clearing up command vs response in install instructions (ros2#2694)

* Clearing up command vs response in install instructions

Co-authored-by: Chris Lalancette <clalancette@gmail.com>

source/Installation/_Apt-Repositories.rst

@@ -4,6 +4,11 @@ First, make sure that the `Ubuntu Universe repository <https://help.ubuntu.com/c
 .. code-block:: bash
 
    apt-cache policy | grep universe
+
+This should output a line like the one below:
+
+.. code-block:: bash
+
     500 http://us.archive.ubuntu.com/ubuntu jammy/universe amd64 Packages
         release v=22.04,o=Ubuntu,a=jammy,n=jammy,l=Ubuntu,c=universe,b=amd64
 
@@ -14,7 +19,6 @@ If you don't see an output line like the one above, then enable the Universe rep
    sudo apt install software-properties-common
    sudo add-apt-repository universe
 
-
 Now add the ROS 2 apt repository to your system.
 First authorize our GPG key with apt.