Document 'How to run rails/rake commands in containers'. (#340)

* Document 'How to run rails/rake commands in containers'.

* Use shorter path to docker-entrypoint.sh.

install/docker-compose.rst

@@ -1,28 +1,28 @@
 Install with Docker Compose
 ***************************
 
-.. warning:: 
+.. warning::
 
-   We currently do not support Docker environments in productive use. 
+   We currently do not support Docker environments in productive use.
    It's no problem if you run Zammad on docker, however, support is only
    provided for Zammad as application!
 
 .. note::
 
-   Docker Compose environments require deeper system know how. 
-   If you're not too familiar with Docker and the way it works, you may want 
+   Docker Compose environments require deeper system know how.
+   If you're not too familiar with Docker and the way it works, you may want
    to stick with :doc:`the package installation </install/package/>` instead.
 
-Docker is a container-based software framework for automating deployment of 
-applications. Compose is a tool for defining and running multi-container Docker 
+Docker is a container-based software framework for automating deployment of
+applications. Compose is a tool for defining and running multi-container Docker
 applications.
 
 Zammads docker images are hosted on `Dockerhub`_.
 
 .. _Dockerhub:
    https://hub.docker.com/r/zammad/zammad-docker-compose/
 
-.. warning:: 
+.. warning::
 
    Never use the ``latest`` tag. Use a tag which has a version attached.
 
@@ -31,7 +31,7 @@ Zammads docker images are hosted on `Dockerhub`_.
 Install Docker Environment
 ==========================
 
-This documentation expects you already have a working Docker Compose 
+This documentation expects you already have a working Docker Compose
 environment. You can find the required documentations for these steps below:
 
    * `Docker Engine <https://docs.docker.com/engine/installation/>`_
@@ -78,8 +78,8 @@ host's settings to ensure a clean runtime.
 Step 3: Adjust Environment as needed
 ------------------------------------
 
-In some cases our default environment is not what a docker-compose user is 
-looking for. To remove complexity from this page, we outsourced information on 
+In some cases our default environment is not what a docker-compose user is
+looking for. To remove complexity from this page, we outsourced information on
 this topic.
 
 See :doc:`/install/docker-compose/environment`
@@ -88,12 +88,29 @@ Step 4: Start Zammad using DockerHub images
 -------------------------------------------
 
 .. warning::
-   
-   Before starting your containers ensure to not use default login data for 
+
+   Before starting your containers ensure to not use default login data for
    your Zammad database! See Step 3!
 
 .. code-block:: sh
 
    $ docker compose up -d
 
+.. hint:: **🔧 How to run rails/rake commands in containers**
+
+   The docker entrypoint script sets up environment variables required by Zammad to function properly.
+   That is why calling ``rails`` / ``rake`` on the console should be done via one of the following methods:
+
+   .. code-block:: sh
+
+      $ docker compose run --rm zammad-railsserver rails r '...your rails command here...'
+
+   This will run the command via the docker entrypoint and is recommended. In case you require the use of ``docker exec``, you can use the following command:
+
+   .. code-block:: sh
+
+      $ docker exec zammad-docker-compose-zammad-railsserver-1 /docker-entrypoint.sh rails r '...your rails command here...'
+
+   This will manually invoke the docker entrypoint and pass the desired command to it for execution in the proper environment.
+
 .. include:: /install/includes/next-steps.rst