Add some option documentation

This is a stab at #385, though the wiki should be updated as well.

The only one I didn't really get was SummerBatchMultiplier. I see how it is used, but am not sure why it is necessary (instead of just using SummerParallelism). It seems the two are never used independently of each other.

Feel free to suggest where this can be expanded. Once this is done, we can use the existing documentation etc to update the wiki.