DBRef page: Clarify what DBRefs are useful for earlier on in the page.

Also, use 'related' instead of 'embedded' to avoid confusion with
sub-documents.

Signed-off-by: Sam Kleinman <samk@10gen.com>
DBRefs page: Grammar and wording changes for clarity.

Signed-off-by: Sam Kleinman <samk@10gen.com>
DBRef page: Update a link to the Ruby 'dereference' docs.

The previous anchor is no longer valid.

Signed-off-by: Sam Kleinman <samk@10gen.com>