[aws] correct placement of static instance docs
[aws] correct placement of static instance docs

The example for using MixedInstancePolicy was accidentally placed under
the new section of the docs for using static instance types, instead of
its correct location under the MixedInstancePolicy section.

bskiba/autoscaler,kubernetes/autoscaler,mmerrill3/autoscaler,mmerrill3/autoscaler,kubernetes/autoscaler,bskiba/autoscaler,mmerrill3/autoscaler,kubernetes/autoscaler,kubernetes/autoscaler,mmerrill3/autoscaler,bskiba/autoscaler