Add 'help' and '?' commands

for printing the help text.

cmd/main.go

@@ -128,6 +128,7 @@ Formats:
 
 Commands:
     tool                    tools for working with test2json output
+    help                    print this help next
 `)
 }
 

cmd/testdata/gotestsum-help-text

@@ -32,3 +32,4 @@ Formats:
 
 Commands:
     tool                    tools for working with test2json output
+    help                    print this help next

main.go

@@ -27,6 +27,8 @@ func route(args []string) error {
 	name := args[0]
 	next, rest := cmd.Next(args[1:])
 	switch next {
+	case "help", "?":
+		return cmd.Run(name, []string{"--help"})
 	case "tool":
 		return tool.Run(name+" "+next, rest)
 	default: