Add note about feeds_batch_set().

CHANGELOG.txt

@@ -5,7 +5,10 @@ Feeds 6.x 1.0 xxxxx xx, xxxx-xx-xx
 
 - #600584 alexb: Use Batch API. NOTE: third party plugins/extensions
   implementing FeedsProcessor::process(), FeedsProcessor::clear() or
-  FeedsImporter::expire() need to adjust their implementations.
+  FeedsImporter::expire() need to adjust their implementations. Modules that
+  directly use Feeds' API for importing or clearing sources need may want to
+  use feeds_batch_set() instead of feeds_source()->import() or
+  feeds_source()->clear().
 
 Feeds 6.x 1.0 Alpha 11, 2010-02-10
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