update README

README.rst

@@ -26,13 +26,14 @@ Usage
 ::
 
    import (
-      "github.com/shirou/gopsutil"
-      "fmt"
    	"encoding/json"
+   	"fmt"
+
+   	"github.com/shirou/gopsutil"
    )
 
-  func main(){
-      v, _ := gopsutil.Virtual_memory()
+   func main() {
+   	v, _ := gopsutil.VirtualMemory()
 
    	// return value is struct
    	fmt.Printf("Total: %v, Free:%v, UsedPercent:%f%%\n", v.Total, v.Free, v.UsedPercent)