[processor/cumulativetodelta] Add warning section (open-telemetry#11851)

Add warning section

processor/cumulativetodeltaprocessor/README.md

@@ -1,10 +1,11 @@
 # Cumulative to Delta Processor
 
-| Status                   |           |
-| ------------------------ | --------- |
-| Stability                | [beta]    |
-| Supported pipeline types | metrics   |
-| Distributions            | [contrib] |
+| Status                   |                           |
+|--------------------------|---------------------------|
+| Stability                | [beta]                    |
+| Supported pipeline types | metrics                   |
+| Distributions            | [contrib]                 |
+| Warnings                 | [Statefulness](#warnings) |
 
 ## Description
 
@@ -75,5 +76,10 @@ processors:
         # convert all cumulative sum metrics to delta
 ```
 
+## Warnings
+
+- [Statefulness](https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/standard-warnings.md#statefulness): The cumulativetodelta processor's calculates delta by remembering the previous value of a metric.  For this reason, the calculation is only accurate if the metric is continuously sent to the same instance of the collector.  As a result, the cumulativetodelta processor may not work as expected if used in a deployment of multiple collectors.  When using this processor it is best for the data source to being sending data to a single collector.
+
+
 [beta]: https://github.com/open-telemetry/opentelemetry-collector#beta
 [contrib]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib