Reference to the shredder mitigation process during backfills. (#6233)

* Reference to the shredder mitigation process during backfills.

* missing dash

docs/cookbooks/creating_a_derived_dataset.md

@@ -268,6 +268,12 @@ For our example:
   bqetl backfill create <project>.<dataset>.<table> --start_date=<YYYY-MM-DD> --end_date=<YYYY-MM-DD>
   ```
 
+  - If the backfill requires [shredder_mitigation](https://docs.telemetry.mozilla.org/cookbooks/data_modeling/shredder_mitigation) to maintain metrics stable, use the `--shredder_mitigation` parameter in the backfill command:
+  
+  ```bash
+  bqetl backfill create <project>.<dataset>.<table> --start_date=<YYYY-MM-DD> --end_date=<YYYY-MM-DD> --shredder_mitigation
+  ``` 
+
 2. Fill out the missing details:
   - Watchers: Mozilla Emails for users that should be notified via Slack about backfill progress.
   - Reason: Why are you backfilling this table?