Update dev guide to have GKE cluster install instructions 📝

We had been pointing folks at the knative docs on cluster setup,
(https://github.com/knative/docs/blob/master/docs/install/Knative-with-GKE.md#creating-a-kubernetes-cluster)
but actually the requirements for running a knative cluster are much
more intense than just for running Tekton (they require 10 nodes, I've
been fine with just 3 all this time), so now let's have our own
instructions that we can keep in sync with Tekton.

Plus this way more of the info you need is right there in the dev guide
:)

DEVELOPMENT.md

@@ -91,20 +91,53 @@ configuring Kubernetes resources.
 ## Kubernetes cluster
 
 Docker for Desktop using an edge version has been proven to work for both
-developing and running Pipelines. Your Kubernetes version must be 1.11 or later.
+developing and running Pipelines. The recommended configuration is:
+
+- Kubernetes version 1.11 or later
+- 4 vCPU nodes (`n1-standard-4`)
+- Node autoscaling, up to 3 nodes
+- API scopes for cloud-platform
 
 To setup a cluster with GKE:
 
 1. [Install required tools and setup GCP project](https://github.com/knative/docs/blob/master/docs/install/Knative-with-GKE.md#before-you-begin)
    (You may find it useful to save the ID of the project in an environment
    variable (e.g. `PROJECT_ID`).
-1. [Create a GKE cluster](https://github.com/knative/docs/blob/master/docs/install/Knative-with-GKE.md#creating-a-kubernetes-cluster)
 
-Note that
-[the `--scopes` argument to `gcloud container cluster create`](https://cloud.google.com/sdk/gcloud/reference/container/clusters/create#--scopes)
-controls what GCP resources the cluster's default service account has access to;
-for example to give the default service account full access to your GCR
-registry, you can add `storage-full` to your `--scopes` arg.
+1. Create a GKE cluster (with `--cluster-version=latest` but you can use any version 1.11 or later):
+
+   ```bash
+   export PROJECT_ID=my-gcp-project
+   export CLUSTER_NAME=mycoolcluster
+
+   gcloud container clusters create $CLUSTER_NAME \
+    --enable-autoscaling \
+    --min-nodes=1 \
+    --max-nodes=3 \
+    --scopes=cloud-platform \
+    --enable-basic-auth \
+    --no-issue-client-certificate \
+    --project=$PROJECT_ID \
+    --region=us-central1 \
+    --machine-type=n1-standard-4 \
+    --image-type=cos \
+    --num-nodes=1 \
+    --cluster-version=latest
+   ```
+
+   Note that
+   [the `--scopes` argument to `gcloud container cluster create`](https://cloud.google.com/sdk/gcloud/reference/container/clusters/create#--scopes)
+   controls what GCP resources the cluster's default service account has access to;
+   for example to give the default service account full access to your GCR
+   registry, you can add `storage-full` to your `--scopes` arg.
+
+1. Grant cluster-admin permissions to the current user:
+
+   ```bash
+   kubectl create clusterrolebinding cluster-admin-binding \
+   --clusterrole=cluster-admin \
+   --user=$(gcloud config get-value core/account)
+   ```
 
 ## Environment Setup