docs: add instruction to remove unwanted attributes from systemd logs

docs/best-practices.md

@@ -12,6 +12,7 @@
   - [Fluentd](#fluentd-1)
   - [OpenTelemetry Collector](#opentelemetry-collector-1)
 - [Collect logs from additional files on the Node](#collect-logs-from-additional-files-on-the-node)
+- [Remove attributes from systemd logs](#removing-attributes-from-systemd-logs)
 - [Filtering Prometheus Metrics by Namespace](#filtering-prometheus-metrics-by-namespace)
 - [Modify the Log Level for Falco](#modify-the-log-level-for-falco)
 - [Overriding metadata using annotations](#overriding-metadata-using-annotations)
@@ -353,6 +354,26 @@ In the example above, two internally defined processors were used in metadata pi
 [memory limiter](https://github.com/open-telemetry/opentelemetry-collector/tree/v0.73.0/processor/memorylimiterprocessor). If you need to
 change the parameters of these processors in any way, you can define your own and use them in this pipeline.
 
+## Removing attributes from systemd logs
+
+If you want to remove some attributes from Systemd logs, like for example `PRIORITY` and `SYSLOG_FACILITY`, you can do it the following way:
+
+```yaml
+sumologic:
+  logs:
+    systemd:
+      otelcol:
+        extraProcessors:
+          - transform/cleanup_systemd:
+              log_statements:
+                - context: log
+                  statements:
+                    - delete_key(body, "PRIORITY")
+                    - delete_key(body, "SYSLOG_FACILITY")
+```
+
+**Note: We do not guarantee that the structure of `otellogs.config.merge` will remain the same between minor helm chart versions**
+
 ## Filtering Prometheus Metrics by Namespace
 
 If you want to filter metrics by namespace, it can be done in the prometheus remote write config. Here is an example of excluding kube-state