add documentation

Author: mus65

CONTRIBUTING.md

@@ -34,9 +34,9 @@ The repository makes use of continuous integration (CI) on [AppVeyor](https://ci
 
 ## Good to know
 
-### TraceSource logging
+### Logging
 
-The Debug build of SSH.NET contains rudimentary logging functionality via `System.Diagnostics.TraceSource`. See `Renci.SshNet.Abstractions.DiagnosticAbstraction` for usage examples.
+The tests always log to the console. See the [Logging documentation](https://sshnet.github.io/SSH.NET/logging.html) on how to set a custom `ILoggerFactory`.
 
 ### Wireshark
 

README.md

@@ -62,6 +62,7 @@ The main types provided by this library are:
 ## Additional Documentation
 
 * [Further examples](https://sshnet.github.io/SSH.NET/examples.html)
+* [Logging](https://sshnet.github.io/SSH.NET/logging.html)
 * [API browser](https://sshnet.github.io/SSH.NET/api/Renci.SshNet.html)
 
 ## Encryption Methods

docfx/logging.md

@@ -0,0 +1,10 @@
+Logging
+=================
+
+SSH.NET uses the `Microsoft.Extensions.Logging` API to log diagnostic messages. In order to access the log messages of SSH.NET in your own application for diagnosis, simply register your own `ILoggerFactory` before using the SSH.NET APIs with the following code:
+
+```cs
+SshNetLoggingConfiguration.InitializeLogging(loggerFactory);
+```
+
+All messages by SSH.NET are logged under the `Renci.SshNet` category.