Update doc: v9-version-upgrade (#8388)

CHANGES.md

@@ -22,7 +22,7 @@ Release Notes.
   name doesn't exist in TCP traffic.
 * Upgrade H2 version to 2.0.202 to fix CVE-2021-23463.
 * Extend column name override mechanism working for `ValueColumnMetadata`.
-* Introduce new concept `Layer` and removed `NodeType`. More details refer to [v9-version-upgrade](docs/en/FAQ/v9-version-upgrade.md)
+* Introduce new concept `Layer` and removed `NodeType`. More details refer to [v9-version-upgrade](https://skywalking.apache.org/docs/main/latest/en/faq/v9-version-upgrade/).
 
 #### UI
 

docs/en/FAQ/v9-version-upgrade.md

@@ -12,7 +12,7 @@ The compatibility with previous releases is as below.
 3. LAL: [Extractor](../../../docs/en/concepts-and-designs/lal.md) add function `layer`. If don't set it manual, the default layer is `GENERAL` and the logs from `ALS` the
    default layer is `mesh`.
 4. Storage：add `service_id`， `short_name` and `layer` columns to table `ServiceTraffic`， add `layer` column to table `InstanceTraffic`.
-   These data would be incompatible with previous in some storage, including H2/OpenSearch/MySQL/TiDB/InfluxDB/PostgreSQL.
+   These data would be incompatible with previous in some storage, including H2/MySQL/TiDB/InfluxDB/PostgreSQL/IoTDB.
    Make sure to remove the older `ServiceTraffic` and `InstanceTraffic` tables before OAP(v9) starts. 
    OAP would generate the new table in the start procedure, and recreate all existing services and instances when traffic comes.
 5. All other metrics are compatible with the previous data format, so you wouldn't lose metrics.