Update entity example to provide contentState instead of blockArray

[kyledetella]

As mentioned (and subsequently fixed in the documentation) by issues #28, #30, and #43 createFromRaw returns an Array of ContentBlock objects. This updates the entity example to reflect those changes.

[hellendag]

convertFromRaw returns a ContentState as of 844b85e.

This example was fixed in a followup by ee082fa.

Master is currently correct -- the documentation is incorrect and needs to be updated. I'll fix that up.