Add NLogLoggerProvider documentation.

Author: bgrainger

docs/UsingNLogLogging.md

@@ -0,0 +1,7 @@
+## How to Use
+
+To integrate MySqlConnector with [NLog](http://nlog-project.org/), add the following line of code to your application startup routine (before any `MySqlConnector` objects have been used):
+
+```
+MySqlConnectorLogManager.Provider = new NLogLoggerProvider();
+```