Add missing things to release notes [ci skip]

- https://github.com/rails/rails/pull/18721
- https://github.com/rails/rails/pull/11898
- https://github.com/rails/rails/pull/18194
- https://github.com/rails/rails/pull/18225
- https://github.com/rails/rails/pull/18244
- edc2b77187
- https://github.com/rails/rails/pull/19686

guides/source/5_0_release_notes.md

@@ -371,6 +371,9 @@ Please refer to the [Changelog][action-pack] for detailed changes.
     at the controller level.
     ([Pull Request](https://github.com/rails/rails/pull/24866))
 
+*   Discarded flash messages get removed before storing into session.
+    ([Pull Request](https://github.com/rails/rails/pull/18721))
+
 Action View
 -------------
 
@@ -676,6 +679,20 @@ Please refer to the [Changelog][active-record] for detailed changes.
     To enable, set `prepared_statements: true` in config/database.yml.
     ([Pull Request](https://github.com/rails/rails/pull/23461))
 
+*   Added ability to call `ActionRecord::Relation#update` on relation objects
+    which will run validations on callbacks on all objects in the relation.
+    ([Pull Request](https://github.com/rails/rails/pull/11898))
+
+*   Added `:touch` option to the `save` method so that records can be saved without
+    updating timestamps.
+    ([Pull Request](https://github.com/rails/rails/pull/18225))
+
+*   Added expression indexes and operator classes support for PostgreSQL.
+    ([commit](https://github.com/rails/rails/commit/edc2b7718725016e988089b5fb6d6fb9d6e16882))
+
+*   Added `:index_errors` option to add indexes to errors of nested attributes.
+    ([Pull Request](https://github.com/rails/rails/pull/19686))
+
 Active Model
 ------------
 
@@ -691,6 +708,9 @@ Please refer to the [Changelog][active-model] for detailed changes.
     [activemodel-serializers-xml](https://github.com/rails/activemodel-serializers-xml) gem.
     ([Pull Request](https://github.com/rails/rails/pull/21161))
 
+*   Removed `ActionController::ModelNaming` module.
+    ([Pull Request](https://github.com/rails/rails/pull/18194))
+
 ### Deprecations
 
 *   Deprecated returning `false` as a way to halt Active Model and
@@ -797,6 +817,9 @@ Please refer to the [Changelog][active-support] for detailed changes.
 *   Removed deprecated `ThreadSafe::Cache`. Use `Concurrent::Map` instead.
     ([Pull Request](https://github.com/rails/rails/pull/21679))
 
+*   Removed `Object#itself` as it is implemented in Ruby 2.2.
+    ([Pull Request](https://github.com/rails/rails/pull/18244))
+
 ### Deprecations
 
 *   Deprecated `MissingSourceFile` in favor of `LoadError`.