Added first draft of Rails 5.2 release notes [ci skip]

guides/source/5_2_release_notes.md

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+**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.**
+
+Ruby on Rails 5.2 Release Notes
+===============================
+
+Highlights in Rails 5.2:
+
+* Active Storage
+* Redis Cache Store
+* HTTP/2 Early hints support
+* Credentials
+
+These release notes cover only the major changes. To learn about various bug
+fixes and changes, please refer to the change logs or check out the [list of
+commits](https://github.com/rails/rails/commits/5-2-stable) in the main Rails
+repository on GitHub.
+
+--------------------------------------------------------------------------------
+
+Upgrading to Rails 5.2
+----------------------
+
+If you're upgrading an existing application, it's a great idea to have good test
+coverage before going in. You should also first upgrade to Rails 5.1 in case you
+haven't and make sure your application still runs as expected before attempting
+an update to Rails 5.2.
+
+
+Major Features
+--------------
+
+### Active Storage
+
+[README](https://github.com/rails/rails/blob/d3893ec38ec61282c2598b01a298124356d6b35a/activestorage/README.md)
+
+### Redis Cache Store
+
+[Pull Request](https://github.com/rails/rails/pull/31134)
+
+
+### HTTP/2 Early hints support
+
+[Pull Request](https://github.com/rails/rails/pull/30744)
+
+
+### Credentials
+
+[Pull Request](https://github.com/rails/rails/pull/30067)
+
+
+Incompatibilities
+-----------------
+
+ToDo
+
+Railties
+--------
+
+Please refer to the [Changelog][railties] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Action Cable
+-----------
+
+Please refer to the [Changelog][action-cable] for detailed changes.
+
+### Notable changes
+
+ToDo
+
+Action Pack
+-----------
+
+Please refer to the [Changelog][action-pack] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Deprecations
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Action View
+-------------
+
+Please refer to the [Changelog][action-view] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Deprecations
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Action Mailer
+-------------
+
+Please refer to the [Changelog][action-mailer] for detailed changes.
+
+### Notable changes
+
+ToDo
+
+Active Record
+-------------
+
+Please refer to the [Changelog][active-record] for detailed changes.
+
+ToDo
+
+### Deprecations
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Active Model
+------------
+
+Please refer to the [Changelog][active-model] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Active Storage
+--------------
+
+Please refer to the [Changelog][active-support] for detailed changes.
+
+### Notable changes
+
+ToDo
+
+Active Support
+--------------
+
+Please refer to the [Changelog][active-support] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Deprecations
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Active Job
+-----------
+
+Please refer to the [Changelog][active-job] for detailed changes.
+
+### Removals
+
+ToDo
+
+### Notable changes
+
+ToDo
+
+Credits
+-------
+
+See the
+[full list of contributors to Rails](http://contributors.rubyonrails.org/) for
+the many people who spent many hours making Rails, the stable and robust
+framework it is. Kudos to all of them.
+
+[railties]:       https://github.com/rails/rails/blob/5-2-stable/railties/CHANGELOG.md
+[action-pack]:    https://github.com/rails/rails/blob/5-2-stable/actionpack/CHANGELOG.md
+[action-view]:    https://github.com/rails/rails/blob/5-2-stable/actionview/CHANGELOG.md
+[action-mailer]:  https://github.com/rails/rails/blob/5-2-stable/actionmailer/CHANGELOG.md
+[action-cable]:   https://github.com/rails/rails/blob/5-2-stable/actioncable/CHANGELOG.md
+[active-record]:  https://github.com/rails/rails/blob/5-2-stable/activerecord/CHANGELOG.md
+[active-model]:   https://github.com/rails/rails/blob/5-2-stable/activemodel/CHANGELOG.md
+[active-storage]: https://github.com/rails/rails/blob/5-2-stable/activestorage/CHANGELOG.md
+[active-support]: https://github.com/rails/rails/blob/5-2-stable/activesupport/CHANGELOG.md
+[active-job]:     https://github.com/rails/rails/blob/5-2-stable/activejob/CHANGELOG.md