Update release docs

docs/topics/3.4-announcement.md

@@ -119,7 +119,7 @@ The following versions of Python and Django are now supported:
 The 3.4 release includes very limited deprecation or behavioral changes, and
 should present a straightforward upgrade.
 
-#### Use fields or exclude on serializer classes.
+### Use fields or exclude on serializer classes.
 
 The following change in 3.3.0 is now escalated from "pending deprecation" to
 "deprecated". Its usage will continue to function but will raise warnings:
@@ -128,7 +128,7 @@ The following change in 3.3.0 is now escalated from "pending deprecation" to
 option, or an `exclude` option. The `fields = '__all__'` shortcut may be used
 to explicitly include all fields.
 
-#### Microsecond precision when returning time or datetime
+### Microsecond precision when returning time or datetime.
 
 Using the default JSON renderer and directly returning a `datetime` or `time`
 instance will now render with microsecond precision (6 digits), rather than
@@ -145,6 +145,22 @@ and `TIME_FORMAT` settings.
 The renderer behavior can be modified by setting a custom `encoder_class`
 attribute on a `JSONRenderer` subclass.
 
+### Relational choices no longer displayed in OPTIONS requests.
+
+Making an `OPTIONS` request to views that have a serializer choice field
+will result in a list of the available choices being returned in the response.
+
+In cases where there is a relational field, the previous behavior would be
+to return a list of available instances to choose from for that relational field.
+
+In order to minimise exposed information the behavior now is to *not* return
+choices information for relational fields.
+
+If you want to override this new behavior you'll need to [implement a custom
+metadata class][metadata].
+
+See [issue #3751][gh3751] for more information on this behavioral change.
+
 ---
 
 ## Other improvements
@@ -170,3 +186,5 @@ The full set of itemized release notes [are available here][release-notes].
 [api-clients]: api-clients.md
 [milestone]: https://github.com/tomchristie/django-rest-framework/milestone/35
 [release-notes]: release-notes#34
+[metadata]: ../../api-guide/metadata/#custom-metadata-classes
+[gh3751]: https://github.com/tomchristie/django-rest-framework/issues/3751