added warning about storage events
added warning about storage events

For those comparing against things like collection-hooks, I thought it would be helpful to highlight that the events are only relative to Class operations and not operations on the underlying collections.
MasterAM/meteor-astronomy,henry-hz/meteor-astronomy,sekmet/meteor-astronomy,jakobrosenberg/meteor-astronomy,jagi/meteor-astronomy,tdamsma/meteor-astronomy,ribbedcrown/meteor-astronomy,awei01/meteor-astronomy