Add stress-ng in required package

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

README.md

@@ -120,7 +120,8 @@ Now, we can install some tools that will be used in the next steps:
 $ sudo apt update
 $ sudo apt install alsa-utils pulseaudio-utils \
                    pipewire-jack sndfile-tools \
-                   psmisc graphviz python3 python3-matplotlib
+                   psmisc graphviz python3 python3-matplotlib \
+                   stress-ng
 ```
 - **alsa-utils** will be used to test sound cards directly using ALSA.
 - **pulseaudio-utils** gives us `pactl` to check if pipewire is running.
@@ -134,6 +135,7 @@ $ sudo apt install alsa-utils pulseaudio-utils \
      into png files to represent the PipeWire graph.
 - **python3** to execute python test scripts.
 - **python3-matplotlib** to generate graph from results.
+- **stress-ng** to simulate a high system load.
 
 
 If the linux kernel is recent enough, you should have sound cards registrered: