Link to official, up-to-date Docker Hub image: prosodyim/prosody

- Official, automated image builds are published as `prosodyim/prosody` on Docker Hub.
- This commit updates links to the published image in `README.md`.
- Still mentioning the outdated `prosody/prosody` image, because they are both official accounts but have confusing naming.
- Adding or updating other documentation would also be helpful.
  - The information page(s) for both Docker Hub images.
  - Links to the outdated Docker Hub image, for example in the Github repository sidebar information.
- Links to alternative `Dockerfile` implementations are moved below the documentation for this repository.

Closes #72.

Usage example:

```shell
docker image pull prosodyim/prosody:13.0

podman image pull docker.io/prosodyim/prosody:13.0
```

See

- https://github.com/prosody/prosody-docker/issues/72
- https://hub.docker.com/r/prosodyim/prosody
- https://hub.docker.com/r/prosody/prosody

README.md

@@ -2,15 +2,10 @@
 
 This is the Prosody Docker image building repository. It is used by our build server to build and publish Docker images for stable releases and nightly builds.
 
-There are many alternative Dockerfiles for Prosody available if this one
-does not suit your needs:
-
-  - [OpusVL/prosody-docker](https://github.com/OpusVL/prosody-docker/)
-  - [unclev/prosody-docker-extended](https://github.com/unclev/prosody-docker-extended)
-
 ## Published images
 
-For images please see here: [Prosody on Docker](https://hub.docker.com/r/prosody/prosody/).
+- **[Docker Hub image prosodyim/prosody](https://hub.docker.com/r/prosodyim/prosody): official images, up-to-date, automated builds.**
+- ~~[Docker Hub image prosody/prosody](https://hub.docker.com/r/prosody/prosody)~~: official images, outdated, manual builds.
 
 ## Running
 
@@ -110,3 +105,11 @@ docker run -it \
 ```bash
 docker build --build-arg PROSODY_PACKAGE=prosody-0.12 -t prosody/prosody:0.12 .
 ```
+
+## Alternative Dockerfiles
+
+There are many alternative Dockerfiles for Prosody available if this one
+does not suit your needs:
+
+  - [OpusVL/prosody-docker](https://github.com/OpusVL/prosody-docker/)
+  - [unclev/prosody-docker-extended](https://github.com/unclev/prosody-docker-extended)