link to element-docker-demo from contrib/docker* (#17953)

Author: ara4n

changelog.d/17953.doc

@@ -0,0 +1 @@
+Link to element-docker-demo from contrib/docker*.

contrib/docker/README.md

@@ -30,3 +30,6 @@ docker-compose up -d
 ### More information
 
 For more information on required environment variables and mounts, see the main docker documentation at [/docker/README.md](../../docker/README.md)
+
+**For a more comprehensive Docker Compose example showcasing a full Matrix 2.0 stack, please see
+https://github.com/element-hq/element-docker-demo**

contrib/docker_compose_workers/README.md

@@ -8,6 +8,9 @@ All examples and snippets assume that your Synapse service is called `synapse` i
 
 An example Docker Compose file can be found [here](docker-compose.yaml).
 
+**For a more comprehensive Docker Compose example, showcasing a full Matrix 2.0 stack (originally based on this
+docker-compose.yaml), please see https://github.com/element-hq/element-docker-demo**
+
 ## Worker Service Examples in Docker Compose
 
 In order to start the Synapse container as a worker, you must specify an `entrypoint` that loads both the `homeserver.yaml` and the configuration for the worker (`synapse-generic-worker-1.yaml` in the example below). You must also include the worker type in the environment variable `SYNAPSE_WORKER` or alternatively pass `-m synapse.app.generic_worker` as part of the `entrypoint` after `"/start.py", "run"`).