Improve release notes.

docs/changelog/103374.yaml

@@ -3,3 +3,14 @@ summary: Cut over stored fields to ZSTD for compression
 area: Search
 type: enhancement
 issues: []
+highlight:
+  title: Stored fields are now compressed with ZStandard instead of LZ4/DEFLATE
+  body: |-
+    Stored fields are now compressed by splitting documents into blocks, which
+    are then compressed independently with ZStandard. `index.codec: default`
+    (default) uses blocks of at most 14kB or 128 documents compressed with level
+    0, while `index.codec: best_compression` uses blocks of at most 240kB or
+    2048 documents compressed at level 3. On most datasets that we tested
+    against, this yielded storage improvements in the order of 10%, slightly
+    faster indexing and similar retrieval latencies.
+  notable: true