HSEARCH-1273 Adding tip about default spatial field name org.hibernate.s...

...earch.annotations.Spatial.COORDINATES_DEFAULT_FIELD.

Also reviewing and fine tuning rest of spatial chapter.
I think the point of the original text was "combine ... with..." being the two concepts
 - fulltext queries
 - distance restrictions

But here:

    With the spatial extensions you can combine fulltext queries distance restrictions

Some conjuction went missing ?