Moving Kite Dataset API info from old guide per CDK-753.

Link to the old guide from which this came. This is just shards of information brought forward so they're not lost. This info should be woven into the samples before 1.0.

http://kitesdk.org/docs/current/kite-data/guide.html
This should actually use the copy constructor for the builder:

```java
DatasetDescriptor updatedDescriptor = new DatasetDescriptor.Builder(originalDescriptor)
    .schemaUri("resource:partitionedProduct_v2.avsc")
    .build()
```

This copies all of the settings from the old descriptor so that the new one is identical except for the changed values.