Added kustomize base files (#1800)

kustomize/README.md

@@ -0,0 +1,22 @@
+This directory provides a base to use with [kubectl kustomize](https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/).
+
+## Example overlay content
+
+### kustomization.yml
+```yaml
+nameSuffix: "-forge"
+commonLabels:
+  server: forge
+bases:
+  - https://github.com/itzg/docker-minecraft-server.git/kustomize/base
+configMapGenerator:
+  - name: mc
+    envs:
+      - mc.env
+```
+
+### mc.env
+```
+EULA=true
+TYPE=FORGE
+```