Merge pull request #16592 from aditya-kapoor/fix-migration-docs

[ci skip] correct docs about the migration generation

activerecord/lib/active_record/migration.rb

@@ -161,21 +161,14 @@ def initialize
   # in the <tt>db/migrate/</tt> directory where <tt>timestamp</tt> is the
   # UTC formatted date and time that the migration was generated.
   #
-  # You may then edit the <tt>up</tt> and <tt>down</tt> methods of
-  # MyNewMigration.
-  #
   # There is a special syntactic shortcut to generate migrations that add fields to a table.
   #
   #   rails generate migration add_fieldname_to_tablename fieldname:string
   #
   # This will generate the file <tt>timestamp_add_fieldname_to_tablename</tt>, which will look like this:
   #   class AddFieldnameToTablename < ActiveRecord::Migration
-  #     def up
-  #       add_column :tablenames, :fieldname, :string
-  #     end
-  #
-  #     def down
-  #       remove_column :tablenames, :fieldname
+  #     def change
+  #       add_column :tablenames, :field, :string
   #     end
   #   end
   #