Fix wrong comment

examples/ReadWrite/ReadWrite.ino

@@ -55,8 +55,7 @@ void setup()
   }
   Serial.println("initialization done.");
   
-  // open the file. note that only one file can be open at a time,
-  // so you have to close this one before opening another.
+  // open the file. 
   myFile = SD.open("test.txt", FILE_WRITE);
   
   // if the file opened okay, write to it: