add deprecated notice to README

exporter/prometheusremotewriteexporter/README.md

@@ -59,7 +59,7 @@ The following settings can be optionally configured:
   - `enabled` (default = false): If `enabled` is `true`, all the resource attributes will be converted to metric labels by default.
 - `target_info`: customize `target_info` metric
   - `enabled` (default = true): If `enabled` is `true`, a `target_info` metric will be generated for each resource metric (see https://github.com/open-telemetry/opentelemetry-specification/pull/2381).
-- `export_created_metric`:
+- `export_created_metric` (deprecated):
   - `enabled` (default = false): If `enabled` is `true`, a `_created` metric is
     exported for Summary, Histogram, and Monotonic Sum metric points if
     `StartTimeUnixNano` is set.