docs: add missing "method"

Author: kenjis

user_guide_src/source/models/model.rst

@@ -738,7 +738,7 @@ points in the model's execution can be affected, each through a class property:
 Defining Callbacks
 ==================
 
-You specify the callbacks by first creating a new class method in your model to use. This class will always
+You specify the callbacks by first creating a new class method in your model to use. This class method will always
 receive a ``$data`` array as its only parameter. The exact contents of the ``$data`` array will vary between events, but
 will always contain a key named **data** that contains the primary data passed to the original method. In the case
 of the insert* or update* methods, that will be the key/value pairs that are being inserted into the database. The