adds to documentation around importing

I ran into some slow indexing with my app and found the vanilla way of importing to be too slow, but didn't see any mention of alternatives in the documentation. I later see #54 as a possible solution, only after reaching a similar conclusion through my own muddling about. I figured it made sense for the documentation to expand upon this, and save future users the same trouble. I pondered if maybe there was a better way to import out of the box too -- or maybe improve the `import` method; but this seemed like a simpler step.