Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField

docs/topics/class-based-views/generic-display.txt

@@ -104,7 +104,7 @@ We'll be using these models::
     class Book(models.Model):
         title = models.CharField(max_length=100)
         authors = models.ManyToManyField('Author')
-        publisher = models.ForeignKey(Publisher)
+        publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE)
         publication_date = models.DateField()
 
 Now we need to define a view::

docs/topics/class-based-views/generic-editing.txt

@@ -204,7 +204,7 @@ the foreign key relation to the model:
 
     class Author(models.Model):
         name = models.CharField(max_length=200)
-        created_by = models.ForeignKey(User)
+        created_by = models.ForeignKey(User, on_delete=models.CASCADE)
 
         # ...