fix: shell completion by adding missing usage message required by spf13/cobra (#1688)

Signed-off-by: DanHam <DanHam@users.noreply.github.com>

cmd/syft/cli/commands.go

@@ -55,6 +55,7 @@ func New() (*cobra.Command, error) {
 
 	// rootCmd is currently an alias for the packages command
 	rootCmd := &cobra.Command{
+		Use:           fmt.Sprintf("%s [SOURCE]", internal.ApplicationName),
 		Short:         packagesCmd.Short,
 		Long:          packagesCmd.Long,
 		Args:          packagesCmd.Args,