README.md in ladder_drive-0.3.1 vs README.md in ladder_drive-0.4.0

@@ -178,9 +178,30 @@
 [![https://gyazo.com/565d24a35887503281a46775f6ccd747](https://i.gyazo.com/565d24a35887503281a46775f6ccd747.gif)](https://gyazo.com/565d24a35887503281a46775f6ccd747)
 
 <!-- [![](http://img.youtube.com/vi/qGbicGLB7Gs/0.jpg)](https://youtu.be/qGbicGLB7Gs) -->
 
 
+# Accessing a device values
+
+You can use LadderDrive as a accessing tool for the PLC device.
+
+You can read/write device like this.
+
+```
+require 'ladder_drive'
+
+plc = LadderDrive::Protocol::Mitsubishi::McProtocol.new host:"192.168.0.10"
+
+plc["M0"] = true
+plc["M0"]         # => true
+plc["M0", 10]     # => [true, false, ..., false]
+
+plc["D0"] = 123
+plc["D0"]       # => 123
+plc["D0", 10] = [0, 1, 2, ..., 9]
+plc["D0".."D9"]   => [0, 1, 2, ..., 9]
+```
+
 # Information related ladder_drive
 
 - [My japanese diary [ladder_drive]](http://diary.itosoft.com/?category=ladder_drive)
 - [Wiki](https://github.com/ito-soft-design/ladder_drive/wiki/)