Add 5.12.4 release notes

release-notes/5.12.4.md

+# CiviCRM 5.12.4
+
+Released April 20, 2019
+
+- **[Synopsis](#synopsis)**
+- **[Bugs resolved](#bugs)**
+- **[Credits](#credits)**
+- **[Feedback](#feedback)**
+
+## <a name="synopsis"></a>Synopsis
+
+| *Does this version...?*                                         |         |
+|:--------------------------------------------------------------- |:-------:|
+| Fix security vulnerabilities?                                   |   no    |
+| Change the database schema?                                     |   no    |
+| Alter the API?                                                  |   no    |
+| Require attention to configuration options?                     |   no    |
+| Fix problems installing or upgrading to a previous version?     |   no    |
+| Introduce features?                                             |   no    |
+| **Fix bugs?**                                                   | **yes** |
+
+## <a name="bugs"></a>Bugs resolved
+
+- **Fix mailing preview fails when viewUrl token present and mailing hash enabled." ([dev/core#891](https://lab.civicrm.org/dev/core/issues/891): [14092](https://github.com/civicrm/civicrm-core/pull/14124))**
+
+## <a name="credits"></a>Credits
+
+This release was developed by the following authors and reviewers:
+
+Wikimedia Foundation - Eileen McNaughton; Australian Greens - Seamus Lee;
+Lighthouse Design and Consulting - Brian Shaughnessy;
+
+## <a name="feedback"></a>Feedback
+
+These release notes are edited by Tim Otten and Andrew Hunt.  If you'd like to
+provide feedback on them, please login to https://chat.civicrm.org/civicrm and
+contact `@agh1`.