write more help text

cmd/primitiveRoot.go

@@ -140,7 +140,11 @@ func primitiveRoot(cmd *cobra.Command, args []string) {
 var primitiveRootCmd = &cobra.Command{
 	Use:   "primitive-root -m M",
 	Short: "Compute a primitive root modulo n",
-	Long:  `Compute a primitive root modulo n.`,
+	Long: `Compute a primitive root modulo n.
+
+This command computes a value g such that, for all integers a coprime to n, g^k = a (mod n) for some k. In other words, this command computes a generator for the multiplicative group of integers modulo n.
+
+For improved performance, provide the prime factorization of the totient of n with the -t flag.`,
 	Run: primitiveRoot,
 }