docs: Add link to Spark pod placement page

Author: Techassi

modules/ROOT/partials/release-notes/release-26.3.adoc

@@ -242,6 +242,7 @@ Implemented in https://github.com/stackabletech/nifi-operator/issues/862[nifi-op
 
 Spark application jobs can now have pod/node affinities.
 Previously only the application driver and executors had a dedicated field for this purpose.
+Consult the xref:spark-k8s:usage-guide/operations/pod-placement.adoc[pod placement guide] for more details.
 Implemented in https://github.com/stackabletech/spark-k8s-operator/issues/639[spark-k8s-operator#639].
 
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