Improve intellisense comment for watchchar event (#83)

***NO_CI***

README.md

@@ -133,7 +133,7 @@ private void DataReceivedNormalEvent(object sender, SerialDataReceivedEventArgs
 #### WatchChar
 
 
-.NET nanoFramework has a specific API to watch for a specific character if present at the end of the transmission.
+.NET nanoFramework has a custom API event to watch for a specific character if present during the transmission.
 
 ```csharp
     port.WatchChar = '\r';
@@ -144,7 +144,7 @@ private void DataReceivedNormalEvent(object sender, SerialDataReceivedEventArgs
 {
     if (e.EventType == SerialData.WatchChar)
     {
-        // We have our special character at the end of the transmission
+        // The specified character was detected when reading from the serialport.
     }
 }
 ```

System.IO.Ports/SerialData.cs

@@ -8,6 +8,11 @@ namespace System.IO.Ports
     /// <summary>
     /// Specifies the type of character that was received on the serial port of the <see cref="SerialPort"/> object.
     /// </summary>
+    /// <remarks>
+    /// This enumeration is used with the <see cref="SerialPort.DataReceived"/> event. 
+    /// You examine the type of character that was received by retrieving the value of the <see cref="SerialDataReceivedEventArgs.EventType"/> property.
+    /// The EventType property contains one of the values from the `SerialData` enumeration.
+    /// </remarks>
     public enum SerialData
     {
         /// <summary>
@@ -16,8 +21,11 @@ namespace System.IO.Ports
         Chars = 1,
 
         /// <summary>
-        ///  The end of file character was received and placed in the input buffer.
+        ///  The `watch` character was received and placed in the input buffer.
         /// </summary>
+        /// <remarks>
+        /// This is only supported on .Net nanoFramework.
+        /// </remarks>
         WatchChar = 2
     }
 }