Expand on within_bounding_box documentation.

Also move it to a new "Advanced Querying" section.

README.rdoc

@@ -118,16 +118,6 @@ To find objects by location, use the following scopes:
   Venue.geocoded                     # venues with coordinates
   Venue.not_geocoded                 # venues without coordinates
 
-You can also restrict the bounds used in location queries via the <tt>within_bounding_box</tt> scope. This
-can have a dramatic effect on query performance, especially when used in conjunction with indexes on the lat,
-lng columns.
-
-  distance = 20
-  center_point = [40.71, 100.23]
-  box = Geocoder::Calculations.bounding_box(center_point, distance)
-  Venue.near(center_point, distance).within_bounding_box(box, distance) # same results as above, potentially faster
-  Venue.within_bounding_box(box, distance) # even faster query, but no distance ordering
-
 With geocoded objects you can do things like this:
 
   obj.nearbys(30)                      # other objects within 30 miles
@@ -211,6 +201,20 @@ For reverse geocoding you can also specify an alternate name attribute where the
   reverse_geocoded_by :coordinates, :address => :loc                # MongoDB
 
 
+== Advanced Querying
+
+When querying for objects (if you're using ActiveRecord) you can also look within a square rather than a radius (circle) by using the <tt>within_bounding_box</tt> scope:
+
+  distance = 20
+  center_point = [40.71, 100.23]
+  box = Geocoder::Calculations.bounding_box(center_point, distance)
+  Venue.within_bounding_box(box, distance)
+
+This can also dramatically improve query performance, especially when used in conjunction with indexes on the latitude/longitude columns. Note, however, that returned results do not include +distance+ and +bearing+ attributes. If you want to improve performance AND have access to distance and bearing info, use both scopes:
+
+  Venue.near(center_point, distance).within_bounding_box(box, distance)
+
+
 == Advanced Geocoding
 
 So far we have looked at shortcuts for assigning geocoding results to object attributes. However, if you need to do something fancy you can skip the auto-assignment by providing a block (takes the object to be geocoded and an array of <tt>Geocoder::Result</tt> objects) in which you handle the parsed geocoding result any way you like, for example: