Merge pull request linode#404 from g1bl3t/lke-changelog-1.20.0

Add changelog update for LKE v1.20.0

Author: bbiggerr

src/content/changelog/lke-1-20-0.md

@@ -0,0 +1,16 @@
+---
+title: Linode Kubernetes Engine v1.20.0
+date: 2021-05-28T05:00:00.000Z
+version: 1.20.0
+changelog:
+  - Linode Kubernetes Engine
+---
+
+### Added
+
+* Add support for Kubernetes v1.21.1.
+
+### Changed
+
+* Change all container image URIs to mirrored repos hosted on the Linode Docker Hub account.
+