Fixed docs typos.

docs/ref/checks.txt

@@ -150,7 +150,7 @@ piggyback on an existing registration.
 
 Fields, models, and model managers all implement a ``check()`` method that is
 already registered with the check framework. If you want to add extra checks,
-you can extend the implemenation on the base class, perform any extra
+you can extend the implementation on the base class, perform any extra
 checks you need, and append any messages to those generated by the base class.
 It's recommended the you delegate each check to a separate methods.
 
@@ -195,7 +195,7 @@ code snippet shows how you can implement this check::
             return []
 
 If you wanted to add checks to a model manager, you would take the same
-approach on your sublass of :class:`~django.db.models.Manager`.
+approach on your subclass of :class:`~django.db.models.Manager`.
 
 If you want to add a check to a model class, the approach is *almost* the same:
 the only difference is that the check is a classmethod, not an instance method::