add tutorial for custom images transformer

examples/transformerconfigs/images/README.md

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+## Images transformations
+
+This tutorial shows how to modify images in resources, and create a custom images transformer configuration.
+
+Create a workspace by
+<!-- @createws @test -->
+```
+DEMO_HOME=$(mktemp -d)
+```
+
+### Adding a custom resource
+
+Consider a Custom Resource Definition(CRD) of kind `MyKind` with field
+- `.spec.runLatest.container.image` referencing an image
+
+Add the following file to configure the images transformer for the CRD:
+
+<!-- @addConfig @test -->
+```
+mkdir $DEMO_HOME/kustomizeconfig
+cat > $DEMO_HOME/kustomizeconfig/mykind.yaml << EOF
+
+images:
+- path: spec/runLatest/container/image
+  kind: MyKind
+EOF
+```
+
+### Apply config
+
+Create a file with some resources that includes an instance of `MyKind`:
+
+<!-- @createResource @test -->
+```
+cat > $DEMO_HOME/resources.yaml << EOF
+
+apiVersion: config/v1
+kind: MyKind
+metadata:
+  name: testSvc
+spec:
+  runLatest:
+    container:
+      image: crd-image
+  containers:
+    - image: docker
+      name: ecosystem
+    - image: my-mysql
+      name: testing-1
+---
+group: apps
+apiVersion: v1
+kind: Deployment
+metadata:
+  name: deploy1
+spec:
+  template:
+    spec:
+      initContainers:
+      - name: nginx2
+        image: my-app
+      - name: init-alpine
+        image: alpine:1.8.0
+EOF
+```
+
+Create a kustomization.yaml referring to it:
+
+<!-- @createKustomization @test -->
+```
+cat > $DEMO_HOME/kustomization.yaml << EOF
+resources:
+- resources.yaml
+
+images:
+- name: crd-image
+  newName: new-crd-image
+  newTag: new-v1-tag
+- name: my-app
+  newName: new-app-1
+  newTag: MYNEWTAG-1
+- name: my-mysql
+  newName: prod-mysql
+  newTag: v3
+- name: docker
+  newName: my-docker2
+  digest: sha256:25a0d4
+EOF
+```
+
+Use the customized transformer configurations by specifying them
+in the kustomization file:
+<!-- @addTransformerConfigs @test -->
+```
+cat >> $DEMO_HOME/kustomization.yaml << EOF
+configurations:
+- kustomizeconfig/mykind.yaml
+EOF
+```
+
+Run `kustomize build` and verify that the images have been updated.
+
+<!-- @build @test -->
+```
+test 1 == \
+$(kustomize build $DEMO_HOME | grep -A 2 ".*image" | grep "new-crd-image:new-v1-tag" | wc -l); \
+echo $?
+```
+
+<!-- @build @test -->
+```
+test 2 == \
+$(kustomize build $DEMO_HOME | grep -A 2 ".*image" | grep "new-app-1:MYNEWTAG-1" | wc -l); \
+echo $?
+```
+
+<!-- @build @test -->
+```
+test 3 == \
+$(kustomize build $DEMO_HOME | grep -A 2 ".*image" | grep "my-docker2@sha" | wc -l); \
+echo $?
+```
+<!-- @build @test -->
+```
+test 4 == \
+$(kustomize build $DEMO_HOME | grep -A 2 ".*image" | grep "prod-mysql:v3" | wc -l); \
+echo $?
+```

examples/transformerconfigs/images/kustomization.yaml

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+resources:
+- resources.yaml
+
+configurations:
+- kustomizeconfig/mykind.yaml
+
+images:
+- name: crd-image
+  newName: new-crd-image
+  newTag: new-v1-tag
+- name: my-app
+  newName: new-app-1
+  newTag: MYNEWTAG-1
+- name: my-mysql
+  newName: prod-mysql
+  newTag: v3
+- name: docker
+  newName: my-docker2
+  digest: sha256:25a0d4

examples/transformerconfigs/images/mykind.yaml

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+images:
+- path: spec/runLatest/container/image
+  kind: MyKind

examples/transformerconfigs/images/resources.yaml

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+apiVersion: config/v1
+kind: MyKind
+metadata:
+  name: testSvc
+spec:
+  runLatest:
+    container:
+      image: crd-image
+  containers:
+    - image: docker
+      name: ecosystem
+    - image: my-mysql
+      name: testing-1
+---
+group: apps
+apiVersion: v1
+kind: Deployment
+metadata:
+  name: deploy1
+spec:
+  template:
+    spec:
+      initContainers:
+      - name: nginx2
+        image: my-app
+      - name: init-alpine
+        image: alpine:1.8.0