### What changes were proposed in this pull request?
As a followup for #29818, document caveats of using the Arrow selfDestruct option in toPandas, which include:
- toPandas() may be slower;
- the resulting dataframe may not support some Pandas operations due to immutable backing arrays.
### Why are the changes needed?
This will hopefully reduce user confusion as with SPARK-34463.
### Does this PR introduce _any_ user-facing change?
Yes - documentation is updated and a config setting description is updated to clearly indicate the config is experimental.
### How was this patch tested?
This is a documentation-only change.
Closes#31738 from lidavidm/spark-34463.
Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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