Enhanced the docker image update section.

Author: jlesage

README.md

@@ -162,8 +162,19 @@ services:
 
 ## Docker Image Update
 
-If the system on which the container runs doesn't provide a way to easily update
-the Docker image, the following steps can be followed:
+Because features are added, issues are fixed, or simply because a new version
+of the containerized application is integrated, the Docker image is regularly
+updated.  Different methods can be used to update the Docker image.
+
+The system used to run the container may have a built-in way to update
+containers.  If so, this could be your primary way to update Docker images.
+
+An other way is to have the image be automatically updated with [Watchtower].
+Whatchtower is a container-based solution for automating Docker image updates.
+This is a "set and forget" type of solution: once a new image is available,
+Watchtower will seamlessly perform the necessary steps to update the container.
+
+Finally, the Docker image can be manually updated with these steps:
 
   1. Fetch the latest image:
 ```
@@ -177,7 +188,10 @@ docker stop nginx-proxy-manager
 ```
 docker rm nginx-proxy-manager
 ```
-  4. Start the container using the `docker run` command.
+  4. Create and start the container using the `docker run` command, with the
+the same parameters that were used when it was deployed initially.
+
+[Watchtower]: https://github.com/containrrr/watchtower
 
 ### Synology