Updating Readme to make writePoints function work

Hello,

I have tried this example as it is for now. Encountered an error that AddPoint function expects only one argument. Checked you GoDoc and updated the example in your error handling style. It works like this.

client/README.md

@@ -142,12 +142,19 @@ func writePoints(clnt client.Client) {
 			"busy": 100.0 - idle,
 		}
 
-		bp.AddPoint(client.NewPoint(
+		pt, err := client.NewPoint(
 			"cpu_usage",
 			tags,
 			fields,
 			time.Now(),
-		))
+		)
+		
+		if err != nil {
+			log.Fatalln("Error: ", err)
+		}
+
+		bp.AddPoint(pt)
+
 	}
 
 	err := clnt.Write(bp)