Update templating doc:

Signed-off-by: Jacob Weinstock <[email protected]>

docs/Template.md

@@ -4,7 +4,11 @@ For this document we will be explaining how to templatize your Template. This wi
 
 ## Background
 
-In Tinkerbell, we have the concept of a Template. This is a defined as a Kubernetes Custom Resource (CR). It describes the steps that will run during a workflow. Look at the CR Definition (CRD) [here](../config/crd/bases/tinkerbell.org_templates.yaml) and an example Template object [here](../config/crd/examples/template.yaml). We also have the concept of Hardware. This is also a Kubernetes Custom Resource (CR). It describes your physical hardware. Look at the CR Definition (CRD) [here](../config/crd/bases/tinkerbell.org_hardware.yaml) and an example Hardware object [here](../config/crd/examples/hardware.yaml).
+In Tinkerbell, we a use Kubernetes Customer Resources to define our data. This includes Hardware, Template, and Workflow definitions. Understanding these will be important to understanding how to template your Template.
+
+- **Hardware**: describes your physical hardware. See the CRD [here](../config/crd/bases/tinkerbell.org_hardware.yaml) and an example Hardware object [here](../config/crd/examples/hardware.yaml)
+- **Template**: describes the steps that will run during a workflow. See the CRD [here](../config/crd/bases/tinkerbell.org_templates.yaml) and an example Template object [here](../config/crd/examples/template.yaml)
+- **Workflow**: describes the steps that will run during a workflow. See the CRD [here](../config/crd/bases/tinkerbell.org_workflows.yaml) and an example Workflow object [here](../config/crd/examples/workflow.yaml)
 
 ## Templating
 
@@ -24,3 +28,45 @@ Inside of this Template there is the ability to use a templating language to get
 | `spec.Interfaces[].DHCP.Hostname`     | `.Hardware.Interfaces[].DHCP.Hostname`        | string        | `{{ (index .Hardware.Interfaces 0).DHCP.Hostname }}`      |
 | `spec.Interfaces[].DHCP.NameServers`  | `.Hardware.Interfaces[].DHCP.Nameservers`     | string array  | `{{ (index .Hardware.Interfaces 0).DHCP.Nameservers }}`   |
 | `spec.Interfaces[].DHCP.TimeServers`  | `.Hardware.Interfaces[].DHCP.Timeservers`     | string array  | `{{ (index .Hardware.Interfaces 0).DHCP.Timeservers }}`   |
+
+## Including data from a Workflow
+
+Arbitrary data can be included in a Workflow object and then accessed from a Template. This data is set via `spec.hardwareMap` in the Workflow. For example below, `device_1` is the arbitrary key and `3c:ec:ef:4c:4f:54` is the value. It can then be accessed in the Template via `{{ .device_1 }}`. See the example below.
+
+```yaml
+apiVersion: "tinkerbell.org/v1alpha1"
+kind: Workflow
+metadata:
+  name: wf1
+spec:
+  templateRef: debian
+  hardwareRef: sm01
+  hardwareMap:
+    device_1: 3c:ec:ef:4c:4f:54
+```
+
+```yaml
+apiVersion: "tinkerbell.org/v1alpha1"
+kind: Template
+metadata:
+  name: debian
+spec:
+  data: |
+    version: "0.1"
+    name: debian
+    global_timeout: 1800
+    tasks:
+      - name: "os-installation"
+        worker: "{{.device_1}}"
+```
+
+## Templating functions
+
+There are a number of built in functions that Go provides and that can be used in your templating. See [here](https://developer.hashicorp.com/nomad/tutorials/templates/go-template-syntax#function-list). Tinkerbell has also defined a few custom functions that can be used.
+
+| Function Name     | Description | Use     | Examples |
+| -------------     | ----------- | ------- | -------- |
+| `contains`        | Contains returns a bool for whether `substr` is within `s`. | `{{ contains "HELLO" "H" }}` | `contains <s> <substr>` |
+| `hasPrefix`       | hasPrefix returns a bool for whether the string s begins with prefix. | `{{ hasPrefix "HELLO" "HE" }}` | `hasPrefix <s> <prefix>` |
+| `hasSuffix`       | hasSuffix returns a bool for whether the string s ends with suffix. | `{{ hasPrefix "HELLO" "HE" }}` | `hasSuffix <s> <suffix>` |
+| `formatPartition` | formatPartition formats a device path with partition for the specific device type. Supported devices: `/dev/nvme`, `/dev/sd`, `/dev/vd`, `/dev/xvd`, `/dev/hd`. | `{{ formatPartition ( index .Hardware.Disks 0 ) 2 }}` | `formatPartition("/dev/nvme0n1", 0) -> /dev/nvme0n1p1`, `formatPartition("/dev/sda", 1) -> /dev/sda1` |