Create migration.md for 0.3.x (#241)

Create migration.md

website/content/en/docs/Getting Started/latest/migration.md

@@ -0,0 +1,23 @@
+---
+title: "Migration from v0.2.x"
+linkTitle: "Migration from v0.2.x"
+weight: 10
+date: 2020-01-03
+description: >
+    How to migrate from v0.2.x to v0.3.x
+---
+
+### Changes
+
+- new Jenkins Custom Resource Definition version `jenkins.io/v1alpha2`:
+  - `spec.master.masterAnnotations` was deprecated, use `spec.master.annotations`
+  - added `spec.notifications`
+  - added `spec.master.tolerations` (in v0.3.1)
+  - added `spec.master.disableCSRFProtection`
+
+### Migration
+
+- adjust the operator image version, e.g. `image: virtuslab/jenkins-operator:v0.3.1`
+- migrate your Jenkins Custom Resources to `apiVersion: jenkins.io/v1alpha2`, adjust content if necessary
+
+The v0.3.x should work fine with `jenkins.io/v1alpha1`, but we recommend using `jenkins.io/v1alpha2`.