Add some very basic docs for logging changes

docs/development/custom/index.md

@@ -9,4 +9,5 @@ This section describes how to extend **Alliance Auth** with custom apps and serv
     integrating-services
     menu-hooks
     url-hooks
+    logging
 ```

docs/development/custom/logging.md

@@ -0,0 +1,17 @@
+# Logging from Custom Apps
+Alliance Auth provides a logger for use with custom apps to make everyone's life a little easier.
+
+## Using the Extensions Logger
+The extensions logger should not be directly used by custom apps as the error messages logged to it 
+will not be labeled with the correct name. In order to correctly use the extensions logger please follow
+the code below.
+
+```python
+import logging
+
+logger = logging.getLogger('extensions.' + __name__)
+logger.name = __name__
+```
+
+This works by creating a child logger of the extension logger which propagates all log entries
+to the parent (extensions) logger.