Provide better documentation for the various ways to run SQL and consume results

[jraymakers]

There are several options for running SQL and consuming results, with different tradeoffs:

• Materializing versus streaming mode (i.e. stream vs run)
• Manual versus automatic running of tasks (i.e. run or stream vs start or startStream)
• Fetching chunks versus using the reader (i.e. fetchChunk versus the various read methods)
• Value extraction versus conversion to arrays (i.e. DuckDBVector.getItem or DuckDBResultReader.valueversusgetRowsorgetColumns`)

What each of these choices mean, what the tradeoffs are, and how they are expressed in the API should be better documented. This likely involves both additional high-level documentation plus more class and method level documentation, both in doc comments and in some sort of API reference.

[jraymakers]

I've added some new sections to the README that briefly describe all the ways to run SQL and get results. See "Ways to run SQL" and "Ways to get result data". While there can always be more documentation, and I'm sure I'll continue to iterate it over time, this should help fill this gap.