Oops; forgot essential cowsay

This is part of the presentation to demonstrate the `bootc update` flow.

Author: gbraad

containers/Containerfile

@@ -5,3 +5,5 @@ FROM ${BASE_IMAGE}:${BASE_VERSION}
 
 RUN useradd -m -d /var/home/admin -G wheel admin \
     && echo "admin:password" | chpasswd
+
+RUN dnf install -y cowsay