Phrase the message template example as YAML not go

The message template is used in YAML files, not in go code.

Signed-off-by: Michael Bridgen <michael@weave.works>

docs/spec/v1alpha1/imageupdateautomations.md

@@ -231,27 +231,28 @@ func (r Result) Objects() map[ObjectIdentifier][]ImageRef {
 The methods let you range over the objects and images without descending the data structure. Here's
 an example of using the fields and methods in a template:
 
-```go
-commitTemplate := `
-`Automated image update
-
-Automation name: {{ .AutomationObject }}
-
-Files:
-{{ range $filename, $_ := .Updated.Files -}}
-- {{ $filename }}
-{{ end -}}
-
-Objects:
-{{ range $resource, $_ := .Updated.Objects -}}
-- {{ $resource.Kind }} {{ $resource.Name }}
-{{ end -}}
-
-Images:
-{{ range .Updated.Images -}}
-- {{.}}
-{{ end -}}
-`
+```yaml
+spec:
+  commit:
+    messsageTemplate: |
+      Automated image update
+      
+      Automation name: {{ .AutomationObject }}
+      
+      Files:
+      {{ range $filename, $_ := .Updated.Files -}}
+      - {{ $filename }}
+      {{ end -}}
+      
+      Objects:
+      {{ range $resource, $_ := .Updated.Objects -}}
+      - {{ $resource.Kind }} {{ $resource.Name }}
+      {{ end -}}
+      
+      Images:
+      {{ range .Updated.Images -}}
+      - {{.}}
+      {{ end -}}
 ```
 
 ## Status