modify readme.md

Author: 刘建平

README.md

@@ -6,16 +6,11 @@ pidfile package
 ````
 	import "github.com/h2object/pidfile"
 
-	// create pid file 
+	// insert into the process begin 
 	pid, err := pidfile.New("h2object.pid")
 	if err != nil {
 		//....
 	}
-
-
-	// stop pid process
-	if err := pid.Kill(); err != nil {
-		//....
-	}
+	defer pid.Kill()
 
 ````

pidfile.go

@@ -34,7 +34,7 @@ func checkPidFileAlreadyExists(path string) error {
 	if pidString, err := ioutil.ReadFile(path); err == nil {
 		if pid, err := strconv.Atoi(string(pidString)); err == nil {
 			if _, err := os.Stat(filepath.Join("/proc", string(pid))); err == nil {
-				return fmt.Errorf("pid file found, ensure docker is not running or delete %s", path)
+				return fmt.Errorf("pid process is running")
 			}
 		}
 	}