Add default to dns resolve

See https://github.com/ipfs/http-api-spec/pull/41#discussion_r53164737

License: MIT
Signed-off-by: Richard Littauer <richard.littauer@gmail.com>

core/commands/dns.go

@@ -50,7 +50,7 @@ The resolver will give:
 		cmds.StringArg("domain-name", true, false, "The domain-name name to resolve.").EnableStdin(),
 	},
 	Options: []cmds.Option{
-		cmds.BoolOption("recursive", "r", "Resolve until the result is not a DNS link."),
+		cmds.BoolOption("recursive", "r", "Resolve until the result is not a DNS link. Default: false."),
 	},
 	Run: func(req cmds.Request, res cmds.Response) {