add document to describe the provision command (#435)

* add document to describe the provision command

* add text about offline usage and development process

* remove comma

Author: mrIncompetent

cmd/provision/README.md

@@ -0,0 +1,77 @@
+# Provisioning
+
+This command offers all required functionality to provision an host to join a Kubernetes cluster.
+
+The following operating systems are supported
+- Ubuntu 18.04
+- CentOS 7
+- ContainerLinux / CoreOS (Not tested with RedHat CoreOS)
+
+## Requirements
+- The cluster needs to use the bootstrap token authentication
+
+## CLI
+
+```bash
+./provision \
+    --kubelet-version="v1.13.1" \
+    --cloud-provider="openstack" \
+    --cloud-config="/etc/kubernetes/cloud-config" \
+    --token="AAAAAAAAAAAAAAAA" \
+    --ca-cert="/etc/kubernetes/ca.crt"
+```
+
+## Process
+
+Nodes will boot with a cloud-init (Or Ignition) which writes required files & a shell script (called `setup.sh` here).
+
+### cloud-init (Or ignition)
+Parts which will be covered by cloud-init (or Ignition)
+
+- Install SSH keys
+- Configure hostname
+- `ca.crt`
+    The CA certificate which got used to issue the certificates of the API server serving certificates
+- `cloud-config`
+    A optional cloud-config used by the kubelet to interact with the cloud provider.
+- `setup.sh`  
+    Is responsible for downloading the `provision` binary and to execute it.
+    The download of the binary might also be done using built-in `cloud-init` (or Ignition) features
+
+### Provision
+
+The `provision` binary will identify the operating system and execute a set of provisioning steps.
+
+The provisioning process gets separated into 2 phases:
+- Base provisioning
+  Install and configure all required dependencies
+- Join
+  Write & start the kubelet systemd unit
+
+#### Base provisioning
+The following steps belong into the base provisioning:
+- Install required packages (apt & yum action)
+- Configure required kernel parameter (Like ip forwarding, etc.)
+- Configure required kernel modules
+- Disable swap
+- Download & install the CNI plugins
+- Download & Install docker
+- Download Kubelet
+- Install health checks (Kubelet & Docker)
+
+#### Join
+
+This part will:
+- Write & start the kubelet systemd unit 
+
+## Offline usage
+
+The `provision` binary should also be usable for "prebaking" images, which then can be used for offline usage.
+
+## Development process
+
+To make sure the local development version of the `provision` command gets used for new machines created by the local running machine controller,
+a new flag `--provision-source` must be introduced. 
+This flag will instruct the machine controller to download the `provision` binary from the specified location.
+
+For simplicity the `/hack/run-machine-controller.sh` will be updated to include a step which will compile the `provoision` command & upload it to a gcs bucket.