docs: clarify vortex-row is not production-ready (#8949)

Updated the README introduction to explicitly state that `vortex-row` is
"**not ready for production use**"

Signed-off-by: Claude <noreply@anthropic.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: joseph-isaacs

vortex-row/README.md

@@ -1,16 +1,16 @@
 # vortex-row
 
-`vortex-row` provides an experimental row-oriented byte encoder for Vortex arrays. It
-produces byte strings that can be compared lexicographically to sort rows according to the
-configured column ordering.
+`vortex-row` provides an experimental row-oriented byte encoder for Vortex arrays. It is
+**not ready for production use**. It produces byte strings that can be compared
+lexicographically to sort rows according to the configured column ordering.
 
 Only supported Vortex logical types are accepted. Extension types are rejected until their
 logical sort semantics are defined.
 
 ## Experimental Format
 
-The row encoding byte layout is experimental. Its exact bytes, supported type set, and
-edge-case semantics may change between Vortex releases.
+The row encoding byte layout is experimental and not ready for production. Its exact bytes,
+supported type set, and edge-case semantics may change between Vortex releases.
 
 Do not persist row-encoded bytes or use them as a stable interchange format. They are intended
 for internal sort-key and row-key operations where the encoder version, schema, and sort