Update release notes and change log

Documentation/Changelog.md

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   the master. There is also limited capability for rejoining nodes.
 
 For more details, please refer to:
+* [MariaDB MaxScale 2.2.21 Release Notes](Release-Notes/MaxScale-2.2.21-Release-Notes.md)
 * [MariaDB MaxScale 2.2.20 Release Notes](Release-Notes/MaxScale-2.2.20-Release-Notes.md)
 * [MariaDB MaxScale 2.2.19 Release Notes](Release-Notes/MaxScale-2.2.19-Release-Notes.md)
 * [MariaDB MaxScale 2.2.18 Release Notes](Release-Notes/MaxScale-2.2.18-Release-Notes.md)

Documentation/Release-Notes/MaxScale-2.2.21-Release-Notes.md

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+# MariaDB MaxScale 2.2.21 Release Notes
+
+Release 2.2.21 is a GA release.
+
+This document describes the changes in release 2.2.21, when compared to the
+previous release in the same series.
+
+For any problems you encounter, please consider submitting a bug
+report on [our Jira](https://jira.mariadb.org/projects/MXS).
+
+## Bug fixes
+
+* [MXS-2410](https://jira.mariadb.org/browse/MXS-2410) Hangup delivered to wrong DCB
+* [MXS-2366](https://jira.mariadb.org/browse/MXS-2366) Wrong tarball RPATH
+
+## Known Issues and Limitations
+
+There are some limitations and known issues within this version of MaxScale.
+For more information, please refer to the [Limitations](../About/Limitations.md) document.
+
+## Packaging
+
+RPM and Debian packages are provided for supported the Linux distributions.
+
+Packages can be downloaded [here](https://mariadb.com/downloads/mariadb-tx/maxscale).
+
+## Source Code
+
+The source code of MaxScale is tagged at GitHub with a tag, which is identical
+with the version of MaxScale. For instance, the tag of version X.Y.Z of MaxScale
+is `maxscale-X.Y.Z`. Further, the default branch is always the latest GA version
+of MaxScale.
+
+The source code is available [here](https://github.com/mariadb-corporation/MaxScale).