* add a note to the documentation about pre-built HLLSketches
Druid actually supports ingesting a pre-generated sketch column by using
the HLLSketchMerge aggregator. However, this functionality was
previously not made clear in the documentation.
* copyedit from the King's English to American English
* add suggested style changes
Co-authored-by: Charles Smith <techdocsmith@gmail.com>
Co-authored-by: Charles Smith <techdocsmith@gmail.com>