docs: Update structured_metadata.md (#12355)

Co-authored-by: J Stickler <julie.stickler@grafana.com>

docs/sources/send-data/promtail/stages/structured_metadata.md

@@ -14,6 +14,8 @@ modifies the [structured metadata]({{< relref "../../../get-started/labels/struc
 
 {{% admonition type="warning" %}}
 Structured metadata will be rejected by Loki unless you enable the `allow_structured_metadata` per tenant configuration (in the `limits_config`).
+
+Structured metadata was added to chunk format V4 which is used if the schema version is greater or equal to **13**. (See Schema Config for more details about schema versions. )
 {{% /admonition %}}
 
 ## Schema
@@ -47,7 +49,7 @@ For the given pipeline:
 Given the following log line:
 
 ```json
-{"log":"log message\n","stream":"stderr","traceID":"0242ac120002",time":"2019-04-30T02:12:41.8443515Z"}
+{"log":"log message\n","stream":"stderr","traceID":"0242ac120002","time":"2019-04-30T02:12:41.8443515Z"}
 ```
 
 The first stage would extract `stream` with a value of `stderr` and `traceID` with a value of `0242ac120002` into