dsl-spec-node-templates

I think there is room for another more formal example tied to these table here, either add it to the example above
or have something like
```
node_templates:
  node_template_1:
    type: ...
    properties: ...
    instances: ...
    interfaces: ...
    relationships: ...
```
otherwise, it is not immediately clear where can these be used until you look for it in the example below