You may add an optional text information to RAR and ZIP archives. This information is called an archive comment. To add it manually in WinRAR shell mode to the already existing archive use Add archive comment command, to read the comment from a file in the command line - command "c" or switch -z<file>.
You also may specify a comment when archiving files directly in the Archive name and parameters dialog.
If an archive, which contains a comment, is opened in WinRAR and the option "Show archive comment" in General settings dialog is on, the comment window will be displayed to the right of the files list. You may change the width of the comment window, dragging its left border with the mouse.