add more help text

cmd/shoelace.go

@@ -99,10 +99,18 @@ func shoelace(cmd *cobra.Command, args []string) {
 
 // shoelaceCmd represents the shoelace command
 var shoelaceCmd = &cobra.Command{
-	Use:   "shoelace",
+	Use:   "shoelace -f FILE",
 	Short: "Compute the area of a simple polygon from the vertex coordinates",
-	Long:  `Compute the area of a simple polygon from the vertex coordinates.`,
-	Run:   shoelace,
+	Long: `Compute the area of a simple polygon from the vertex coordinates.
+
+Put each point on its own line, with each coordinate separated by whitespace. For example, a file with
+1 6
+3 1
+7 2
+4 4
+8 5
+will output an area of 16.5.`,
+	Run: shoelace,
 }
 
 func init() {