docs: Example showing how to use default settings for workflow spec. …

…Related to #argoproj#2388 (argoproj#2411)

docs/default-workflow-specs.md

@@ -0,0 +1,37 @@
+# Default Workflow Spec
+
+![alpha](assets/alpha.svg)
+
+> v2.7 and after
+
+It's possible to set default workflow specs which will be written to all workflows if the spec of interest is not set. This can be configurated through the 
+workflow controller config [map](../workflow/config/config.go#L11) and the field [DefaultWorkflowSpec](../workflow/config/config.go#L69). 
+
+
+In order to edit the Default workflow spec for a controller, edit the workflow config map: 
+
+
+```bash 
+kubectl edit cm/workflow-controller-configmap
+```
+
+
+As an example the time for a argo workflow to live after finish can be set, in the spec this field is known as ```secondsAfterCompletion``` in the ```ttlStrategy```. Example of how the config map could look with this filed can be found [here](./workflow-controller-configmap.yaml).
+
+In order to test it a example workflow can be submited, in this case the [coinflip example](../examples/coinflip.yaml), the following can be run:
+
+```bash 
+argo submit ./examples/coinflip.yaml
+```
+
+to verify that the the defaultd are set run 
+
+```bash
+argo get [YOUR_ARGO_WORKFLOW_NAME]
+```
+
+You should then see the field, Ttl Strategy populated
+```yaml
+Ttl Strategy:
+ Seconds After Completion: 10
+```

docs/workflow-controller-configmap.yaml

@@ -157,3 +157,8 @@ data:
  # passwordSecret:
  # name: argo-mysql-config
  # key: password
+
+ # default workflow spec, follow the workflow spec, more info: https://github.com/argoproj/argo/blob/master/examples/README.md#the-structure-of-workflow-specs
+ workflowDefaults:
+ ttlStrategy:
+ secondsAfterCompletion: 10