add doc on how to use a custom storage

docs/storages.rst

@@ -31,3 +31,23 @@ Pipeline is also providing a storage that play nicely with staticfiles app
 particularly for development : ::
 
   PIPELINE_STORAGE = 'pipeline.storage.PipelineFinderStorage'
+
+
+Using with other storages
+=========================
+
+You can also use your own custom storage, for example, if you want to use S3 for your assets : ::
+
+  STATICFILES_STORAGE = 'your.app.S3PipelineStorage'
+
+Your storage only need to inherit from ``PipelineMixin`` and/or ``CachedFilesMixin`` : ::
+
+  from staticfiles.storage import CachedFilesMixin
+  
+  from pipeline.storage import PipelineMixin
+  
+  from storages.backends.s3boto import S3BotoStorage
+  
+  
+  class S3PipelineStorage(PipelineMixin, CachedFilesMixin, S3BotoStorage):
+       pass