Fix the documentation

README.md

@@ -22,9 +22,9 @@ This documentation is rudimentary.
   ```python
   from my2to3.trace import tracing_functions, apply_fixers
 
-  # `tracing_function` contains all the functions registered with
-  # `@register_tracing_function`. Add its content to the builtins (or
-  # equivalent) of the component to monkey-patch, e.g.:
+  # `tracing_functions` contains all the functions which trace data at runtime.
+  # Add its content to the builtins (or equivalent) of the component to
+  # monkey-patch, e.g.:
   component_builtins.update({f.__name__: f for f in tracing_functions})
 
   # `name` must be a unique name which represents the code to modify, to easily