Provide a "cheat sheet" for official Tekton releases

Our existing tekton/README.md and the release instructions from plumbing
are excellent resources but they provide a lot of additional context
which isn't strictly useful when someone is just trying to perform an
official release.

This commit introduces a condensed cheat sheet that just lists the steps
to take, in order, when performing an official Tekton Pipelines release.
I wrote and then used these instructions for the 0.11.2 release.

Author: Scott

tekton/release-cheat-sheet.md

@@ -0,0 +1,154 @@
+# Tekton Pipelines Official Release Cheat Sheet
+
+This doc is a condensed version of our [tekton/README.md](./README.md) as
+well as instructions from
+[our plumbing repo](https://github.com/tektoncd/plumbing/tree/master/tekton/resources/release/README.md#create-draft-release).
+
+These steps provide a no-frills guide to performing an official release
+of Tekton Pipelines. To follow these steps you'll need a checkout of
+the pipelines repo, a terminal window and a text editor.
+
+1. `cd` to root of Pipelines git checkout.
+
+2. Point `kubectl` at dogfooding cluster.
+
+    ```bash
+    gcloud container clusters get-credentials dogfooding --zone us-central1-a --project tekton-releases
+    ```
+
+3. Edit `tekton/resources.yaml`. Add pipeline resource for new version.
+
+    ```yaml
+    apiVersion: tekton.dev/v1alpha1
+    kind: PipelineResource
+    metadata:
+      name: # UPDATE THIS. Example: tekton-pipelines-v0-11-2
+    spec:
+      type: git
+      params:
+      - name: url
+        value: https://github.com/tektoncd/pipeline
+      - name: revision
+        value: # UPDATE THIS. Example: 33e0847e67fc9804689e50371746c3cdad4b0a9d
+    ```
+
+4. `kubectl apply -f tekton/resources.yaml`
+
+5. Create environment variables for bash scripts in later steps.
+
+    ```bash
+    VERSION_TAG=# UPDATE THIS. Example: v0.11.2
+    GIT_RESOURCE_NAME=# UPDATE THIS. Example: tekton-pipelines-v0-11-2
+    IMAGE_REGISTRY=gcr.io/tekton-releases
+    ```
+
+6. Confirm commit SHA matches what you want to release.
+
+    ```bash
+    kubectl get pipelineresource "$GIT_RESOURCE_NAME" -o=jsonpath="{'Target Revision: '}{.spec.params[?(@.name == 'revision')].value}{'\n'}"
+    ```
+
+7. Execute the release pipeline.
+
+    **If you are backporting include this flag: `--param=releaseAsLatest="false"`**
+
+    ```bash
+    tkn pipeline start \
+      --param=versionTag="${VERSION_TAG}" \
+      --param=imageRegistry="${IMAGE_REGISTRY}" \
+      --serviceaccount=release-right-meow \
+      --resource=source-repo="${GIT_RESOURCE_NAME}" \
+      --resource=bucket=pipeline-tekton-bucket \
+      --resource=builtBaseImage=base-image \
+      --resource=builtEntrypointImage=entrypoint-image \
+      --resource=builtKubeconfigWriterImage=kubeconfigwriter-image \
+      --resource=builtCredsInitImage=creds-init-image \
+      --resource=builtGitInitImage=git-init-image \
+      --resource=builtControllerImage=controller-image \
+      --resource=builtWebhookImage=webhook-image \
+      --resource=builtDigestExporterImage=digest-exporter-image \
+      --resource=builtPullRequestInitImage=pull-request-init-image \
+      --resource=builtGcsFetcherImage=gcs-fetcher-image \
+      --resource=notification=post-release-trigger \
+    pipeline-release
+    ```
+
+8. Watch logs of pipeline-release.
+
+9. The YAMLs are now released! Anyone installing Tekton Pipelines will now get the new version. Time to create a new GitHub release announcement:
+
+    1. Create TaskRun YAML file to execute create-draft-release Task.
+
+        ```yaml
+        apiVersion: tekton.dev/v1beta1
+        kind: TaskRun
+        metadata:
+          generateName: create-draft-release-run-
+        spec:
+          taskRef:
+            name: create-draft-release
+          params:
+          - name: release-name
+            value: # UPDATE THIS. Example: "Ragdoll Norby"
+          - name: package
+            value: tektoncd/pipeline
+          - name: release-tag
+            value: # UPDATE THIS. Example: v0.11.2
+          - name: previous-release-tag
+            value: # UPDATE THIS. Example: v0.11.1
+          resources:
+            inputs:
+            - name: source
+              resourceRef:
+                name: # UPDATE THIS WITH PIPELINE RESOURCE YOU CREATED EARLIER. Example: tekton-pipelines-v0-11-2
+            - name: release-bucket
+              resourceRef:
+                name: # UPDATE THIS WITH BUCKET RESOURCE NAME FROM EARLIER. Example: tekton-release-bucket-pipeline
+        ```
+
+    2. Save as `create-draft-release-run.yaml`
+
+    3. Run Draft Release Task.
+
+        ```bash
+        kubectl create -f ./create-draft-release-run.yaml
+        ```
+
+    4. Watch logs of create-draft-release TaskRun for errors.
+
+        ```bash
+        tkn tr logs -f create-draft-release-run-# this will end with a random string of characters
+        ```
+
+    5. On successful completion, a URL will be logged. Visit that URL and sort the
+    release notes. **Double-check that the list of commits here matches your expectations
+    for the release.** You might need to remove incorrect commits or copy/paste commits
+    from the release branch. Refer to previous releases to confirm the expected format.
+
+    6. Publish the GitHub release once all notes are correct and in order.
+
+10. Edit `README.md` on `master` branch, add entry to docs table with latest release links.
+
+11. Push & make PR for updated `README.md`
+
+12. **Important: Stop pointing `kubectl` at dogfooding cluster.**
+
+    ```bash
+    kubectl config use-context my-dev-cluster
+    ```
+
+13. Test release that you just made.
+
+    ```bash
+    # Test latest
+    kubectl apply --filename https://storage.googleapis.com/tekton-releases/pipeline/latest/release.yaml
+    ```
+
+    ```bash
+    # Test backport
+    kubectl apply --filename https://storage.googleapis.com/tekton-releases/pipeline/previous/v0.11.2/release.yaml
+    ```
+
+14. Announce the release in Slack channels #general and #pipelines.
+
+Congratulations, you're done!