📖 Add prerequisite helm charts to README.md for cronjob tutorial

[TylerJGabb]

Problem:

When following the tutorial for docs/book/src/cronjob-tutorial/testdata/project I ran into issues caused by the lack of operators in my cluster.

Solution:

I'm adding some documentation to the readme to help anyone following the tutorial understand what prerequisites are required for the cluster that they plan to use when following the cronjob tutorial.

Motivation:

Following the cronjob tutorial to the end, after running make manifests and make install, I attempted to run make deploy

First I was confronted with missing CRDs

resource mapping not found for name: "project-serving-cert" namespace: "project-system" from "STDIN": no matches for kind "Certificate" in version "cert-manager.io/v1"
ensure CRDs are installed first
resource mapping not found for name: "project-selfsigned-issuer" namespace: "project-system" from "STDIN": no matches for kind "Issuer" in version "cert-manager.io/v1"
ensure CRDs are installed first
resource mapping not found for name: "project-controller-manager-metrics-monitor" namespace: "project-system" from "STDIN": no matches for kind "ServiceMonitor" in version "monitoring.coreos.com/v1"
ensure CRDs are installed first
make: *** [deploy] Error 1

Which was remedied by installing cert-manager.

Then I ran make deploy again, after which I encountered this

resource mapping not found for name: "project-serving-cert" namespace: "project-system" from "STDIN": no matches for kind "Certificate" in version "cert-manager.io/v1"
ensure CRDs are installed first
resource mapping not found for name: "project-selfsigned-issuer" namespace: "project-system" from "STDIN": no matches for kind "Issuer" in version "cert-manager.io/v1"
ensure CRDs are installed first
resource mapping not found for name: "project-controller-manager-metrics-monitor" namespace: "project-system" from "STDIN": no matches for kind "ServiceMonitor" in version "monitoring.coreos.com/v1"
ensure CRDs are installed first
make: *** [deploy] Error 1

Which was remedied by installing kube-prometheus-stack

I was then able to run make deploy successfully.

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• ✅ login: TylerJGabb / name: Tyler Gabb (71e71b7, daedf69)

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Hi @TylerJGabb. Thanks for your PR.

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This pull-request has been approved by: TylerJGabb
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