Modified link to docker docs for persistent data and updated the Arbitrary user title

Author: ichim-david

docs/install/containers/images/backend.md

@@ -31,7 +31,7 @@ There are several ways to store data used by applications that run in Docker con
 
 We encourage users of the `Plone` images to familiarize themselves with the options available.
 
-[The Docker documentation](https://docs.docker.com/) is a good starting point for understanding the different storage options and variations.
+[The Docker documentation](https://docs.docker.com/guides/docker-concepts/running-containers/persisting-container-data) is a good starting point for understanding the different storage options and variations.
 
 
 ## Configuration Variables
@@ -375,7 +375,7 @@ when Plone starts.
 ## Advanced usage
 
 
-### Arbitrary `--user`
+### Arbitrary `--user` and persisting data using `docker volumes`
 
 This image supports running as a (mostly) arbitrary user via `--user` on `docker run`, as long as the owner of `/data` matches: