docs: docker secrets available in v5.2.0

docs/sources/installation/docker.md

@@ -132,6 +132,8 @@ docker run -d --user $ID --volume "$PWD/data:/var/lib/grafana" -p 3000:3000 graf
 
 ## Reading secrets from files (support for Docker Secrets)
 
+> Available in v5.2.0 and later
+
 It's possible to supply Grafana with configuration through files. This works well with [Docker Secrets](https://docs.docker.com/engine/swarm/secrets/) as the secrets by default gets mapped into `/run/secrets/<name of secret>` of the container.
 
 You can do this with any of the configuration options in conf/grafana.ini by setting `GF_<SectionName>_<KeyName>_FILE` to the path of the file holding the secret.