Add some documentation

app/decorators.py

@@ -16,7 +16,14 @@ def admin_required(f):
 
 
 def background(f):
-    ''' This decorator executes a function in a Thread '''
+    '''
+    ' This decorator executes a function in a Thread.
+    ' Decorated functions need to be executed within a code block where an
+    ' app context exists.
+    '
+    ' NOTE: An app object is passed as a keyword argument to the decorated
+    '       function.
+    '''
     @wraps(f)
     def wrapped(*args, **kwargs):
         kwargs['app'] = current_app._get_current_object()