Document development workflow

[invidian]

It would be good to document how to develop this provider.

So far, I figured out that one needs to follow https://cluster-api.sigs.k8s.io/developer/tilt.html (with fixes added in #12).

I still didn't figure out how to put TINKERBELL_GRPC_AUTHORITY and TINKERBELL_CERT_URL into it, right now I just edit the secret which contains them and restart the pod manually.

Next thing we should figure out how to setup Tinkerbell for testing it. @detiber pointed me to https://github.com/detiber/tink/blob/kindDev/README-TILT.md, so we can run Tinkerbell on the same K8s cluster as the cluster API, but I didn't figure that part yet.

Also, we can consider merging those 2 workflows somehow, so tilt up just works automagically.

Note: cluster-api must be on branch release-0.3 right now.

WIP list of steps:

1. curl -fsSL https://github.com/tilt-dev/tilt/master/scripts/install.sh | bash
2. git clone https://github.com/kubernetes-sigs/cluster-api
3. git clone git@github.com:tinkerbell/cluster-api-provider-tink.git
4. cd cluster-api
5. git checkout release-0.3

cat <<EOF > tilt-settings.json
{
  "default_registry": "quay.io/<your username>",
  "provider_repos": ["../cluster-api-provider-tink"],
  "enable_providers": ["tinkerbell", "docker", "kubeadm-bootstrap", "kubeadm-control-plane"],
  "allowed_contexts": ["<your kubeconfig context to use"]
}
EOF

7. export TINKERBELL_GRPC_AUTHORITY=10.17.3.2:42113 TINKERBELL_CERT_URL=http://10.17.3.2:42114/cert
8. tilt up

Make sure TINKERBELL_GRPC_AUTHORITY and TINKERBELL_CERT_URL points to the running Tinkerbell instance, where your Kubernetes cluster pods can access it.

If all commands above succeeded, Tilt website should be all green and changes to the codebase of the provider should propagate to the cluster.