Updated doc regarding applying extensions for extensible search
Updated doc regarding applying extensions for extensible search

stephenmcm/silverstripe-solr,stephenmcm/silverstripe-solr,stephenmcm/silverstripe-solr,stephenmcm/silverstripe-solr,nyeholt/silverstripe-solr,nyeholt/silverstripe-solr,nyeholt/silverstripe-solr,nyeholt/silverstripe-solr