add some comment

ingredients/core-packages-mandatory.cfg

@@ -10,6 +10,7 @@
 
 %packages --ignoremissing --nocore --exclude-weakdeps # Beginning of the package section. Does not include weak dependencies. Description courtesy of the Fedora project
 
+# Mandatory packages found in hidden `core` group (`dnf group info --hidden core`)
 audit # User space tools for kernel auditing
 basesystem # The skeleton package which defines a simple Fedora system
 bash # The Bourne Again SHell, a command-line interpreter.