docs: added HStoreSerializer to third party serializers

added a reference to django-rest-framework-hstore in docs/api-guide/serializers.md

docs/api-guide/serializers.md

@@ -594,7 +594,13 @@ The [django-rest-framework-mongoengine][mongoengine] package provides a `MongoEn
 
 The [django-rest-framework-gis][django-rest-framework-gis] package provides a `GeoFeatureModelSerializer` serializer class that supports GeoJSON both for read and write operations.
 
+## HStoreSerializer
+
+The [django-rest-framework-hstore][django-rest-framework-hstore] package provides an `HStoreSerializer` to support [django-hstore][django-hstore] `DictionaryField` model field and its `schema-mode` feature.
+
 [cite]: https://groups.google.com/d/topic/django-users/sVFaOfQi4wY/discussion
 [relations]: relations.md
 [mongoengine]: https://github.com/umutbozkurt/django-rest-framework-mongoengine
 [django-rest-framework-gis]: https://github.com/djangonauts/django-rest-framework-gis
+[django-rest-framework-hstore]: https://github.com/djangonauts/django-rest-framework-hstore
+[django-hstore]: https://github.com/djangonauts/django-hstore