Create a new tutorial how to automatic update and cleanup old docker images

docs/content/advanced/maintenance/update-and-cleanup.md

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+# Automatic update
+
+Docker images are handy but it can get a a hassle to keep them updated. Also when a repository is automated you want to get these images when they get out.
+
+There is a nice docker image that solves this issue and can be very helpful. The image is: [v2tec/watchtower](https://hub.docker.com/r/v2tec/watchtower/).
+
+A docker-compose example:
+```yaml
+services:
+  watchtower:
+    restart: always
+    image: v2tec/watchtower:latest
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+```
+
+For more details see the [manual](https://github.com/v2tec/watchtower/blob/master/README.md)
+
+
+***
+
+
+# Automatic cleanup
+
+When you are pulling new images in automaticly it is nice to have them cleaned as well. There is also a docker images for this (from Spotify). The image is: [spotify/docker-gc](https://hub.docker.com/r/spotify/docker-gc/).
+
+A docker-compose example:
+```yaml
+services:
+  docker-gc:
+    restart: always
+    image: spotify/docker-gc:latest
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+```
+
+For more details see the [manual](https://github.com/spotify/docker-gc/blob/master/README.md)