Add v0.1.x upgrade documentation

docs/0.1-upgrade.md

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+# v0.1.* Upgrade
+
+The v0.1.* release series is the *only* release series of the MySQL Operator
+which supports MySQL 5.7. InnoDB Group replication and associated tooling has
+been dramatically improved with the GA release of MySQL 8 (8.0.11). As a result
+from the v0.2.0 MySQL Operator release onwards MySQL 8.0.11 is the __minimum
+supported version__.
+
+Due to the complexities of the upgrade path between MySQL 5.7 and MySQL 8 we
+aren't implementing an upgrade path between the v0.1.* and v0.2.* MySQL Operator
+release series.
+
+Instead users need to:
+
+ 1) Backup all MySQL Clusters deployed by the MySQL Operator. NOTE: If you
+    choose to use the inbuilt backup functionality of the MySQL Operator for
+    this you will need to ensure you save the associated MySQLBackup resources
+    locally, update them in line with the v0.2.0 API changes, and the recreate
+    them after installing v0.2.0.
+ 3) Delete the MySQL Operator release
+
+    ```console
+    $ helm delete mysql-operator
+    ```
+    NOTE: You may have named the installed MySQL Operator release something
+    different during installation (see `helm list`).
+ 4) Follow the installation instructions to install v0.2.0 of the MySQL
+    Operator.
+ 5) Create replacement MySQL Clusters using the updated API and restore the
+    backups created in step #1.
+
+## Other Breaking Changes
+
+Additionally, we have taken this opportunity to make a number of breaking
+changes to the MySQL Operator API to improve its usability.
+
+### API Version Downgrade
+
+We have downgraded the API Version from `v1` to `v1alpha1` to enable future
+iteration on the API design (taking advantage of the fact that [Custom Resource
+Definitions can now define multiple versions][1]) and to better reflect the
+stability of the MySQL Operator API.
+
+### Resource Kinds Renamed
+
+Previously the MySQL Operator Custom Resource Kinds were prefixed with MySQL
+(e.g.  `MySQLCluster`). This prefix has been removed, however, the prefix has
+been maintained in the singular/plural names used when interacting via
+`kubectl` (e.g. `kubectl get mysqlclusters`).
+
+### API changes
+
+Numerous fields on all MySQL Operator Custom Resources have been renamed and
+some field types changed. Please review [`pkg/apis/mysql/v1alpha1/types.go`][2]
+as the definitive source of truth and see the updated [`examples/`][3].
+
+[1]: https://kubernetes.io/blog/2018/06/27/kubernetes-1.11-release-announcement/#custom-resource-definitions-can-now-define-multiple-versions
+[2]: https://github.com/oracle/mysql-operator/blob/master/pkg/apis/mysql/v1alpha1/types.go
+[3]: https://github.com/oracle/mysql-operator/tree/master/examples