[chore][logstransformprocessor] Add note about processor not being re…

…leased in contrib (#29275)

An issue was opened recently wondering why this processory was not
available in the contrib release. Since this processor is experimental
and temporary there's no plan to support it long term, so I've added a
note that makes it clear why it's not included in the contrib
distribution releases.

Fixes #29150

processor/logstransformprocessor/README.md

@@ -15,6 +15,7 @@
 <!-- end autogenerated section -->
 
 NOTE - This processor is experimental, with the intention that its functionality will be reimplemented in the [transform processor](../transformprocessor/README.md) in the future.
+For this reason, the processor is not included in the `contrib` distribution.
 
 The logs transform processor can be used to apply [log operators](../../pkg/stanza/docs/operators) to logs coming from any receiver.
 Please refer to [config.go](./config.go) for the config spec.