[autoscale] documentation about load_balancers doesn't match implementation

[radix]

The autoscale.md specifies that you can pass 'load_balancers' as a list of tuples of (load_balancer_id, port), but that syntax doesn't seem to be supported by pyrax.

as per the docstring of _resolve_lbs (which seems to agree with the actual implementation):

    References can be either a dict that matches the structure required by
    the autoscale API, a CloudLoadBalancer instance, or the ID of the load
    balancer.

I don't know if there's a strong use case for supporting the tuple syntax, so maybe the documentation should just be updated.

[EdLeafe]

IRC user 'turinggroup' reported a nearly identical issue today. Bumping this up so that it gets some attention.