grammar touchups, mild rewording in several places

Disclaimer: This is my first pull request ever.  Feel free to disregard any and all of the suggestions embodied herein.

I removed the tabs from the HTML to increase readability and then applied a consistent indent pattern.  These modifications make the changes appear more extensive than they really are.

A further possible improvement might be more explanation around the differences between 2d and 2dsphere.  I know this point caused me a fair amount of confusion.  The MongoDB documentation does not help the situation because it makes 2d indices appear "legacy," as if somehow deprecated.  Indeed, if the application really uses longitude and latitude, the points should probably be in geoJSON format and the index in 2dsphere.  GeoJSON format data does not appear to be supported by 2d indices which further confuses the matter.  Additionally, is the 2d format really confined to the range of values that longitude and latitude are confined to?  If so, that is sort of an odd coordinate system for describing an arbitrary flat plane.  I suspect that MongoDB started with 2d and then developed 2dsphere which would explain the oddity.  I think both applications (geomapping AND mapping a flat plane of your choice) are interesting, but perhaps need to be made more distinct.