Scale factor defined in fig.yml

The scale command is very useful to define a unique docker entry in the fig.yml and scale the number of containers in execution time, but I can't found any way to increase the default number of containers at initial start. There is any way to define it in the fig.yml?

Something like:

```
node:
    build: node
    scale: 3
```

If not exist, I think it could be a nice feature.
