Use "container" instead of Docker when possible in start.md

and add note about DOCKER_HOST environment variable.

Author: rgaiacs

docs/source/start.md

@@ -2,47 +2,64 @@
 
 This tutorial guides you through installing `repo2docker` and building your first environment image.
 
-(install)=
+## Prerequisite
 
-## Install `repo2docker`
+### Python
 
-`repo2docker` requires Python 3.6 or above on Linux and macOS.
+`repo2docker` requires Python 3.6 or above.
 
-:::{admonition} Windows support is experimental
+### Container Engine
 
-This [article about using Windows and the WSL](https://nickjanetakis.com/blog/setting-up-docker-for-windows-and-wsl-to-work-flawlessly) (Windows Subsystem for Linux or
-Bash on Windows) provides additional information about Windows and Docker.
-:::
+`repo2docker` requires a container engine compatible with the specification published by the [Open Container Initiative](https://opencontainers.org/).
 
-### Prerequisite: Install Docker
+#### Docker
 
-Install [Docker](https://www.docker.com), as it is required to build Docker images.
-The [Community Edition](https://docs.docker.com/install/) is available for free.
+```{important}
+Only the [Docker Engine](https://docs.docker.com/engine/) is an open source. [Docker Desktop](https://docs.docker.com/get-started/get-docker/) requires a license.
+```
 
-Recent versions of Docker are recommended.
+Follow [Docker's official installation steps](https://docs.docker.com/get-started/get-docker/).
 
-### Install `repo2docker` with `pip`
+#### Podman
 
-```{warning}
-The name of the package on [PyPI](https://pypi.org/) is [`jupyter-repo2docker`](https://pypi.org/project/jupyter-repo2docker/) instead of `repo2docker`.
-```
+Follow [Podman's official installation steps](https://podman.io/docs/installation).
 
-We recommend installing `repo2docker` with the `pip` tool:
+And configure the `DOCKER_HOST` environment variable following [Podman's official procedure](https://podman-desktop.io/docs/migrating-from-docker/using-the-docker_host-environment-variable#procedure).
 
-```
+(install)=
+
+## Install `repo2docker`
+
+### Install `repo2docker` with `pip`
+
+It is recommend to install `repo2docker` with the `pip` tool:
+
+```bash
 python3 -m pip install jupyter-repo2docker
 ```
 
 (usage)=
 
 ## Build a repository with `repo2docker`
 
-Now that you've installed Docker and `repo2docker`, we can build a repository.
-To do so, follow these steps.
+Now that you've installed a container engine and `repo2docker`, you can build a repository.
+To do so, continue following this guide.
+
+### Start the container engine
+
+Ensure that the container engine is running.
 
-### Start Docker
+#### Docker
 
-Follow the [instructions for starting Docker](https://docs.docker.com/engine/daemon/start/) to start a Docker process.
+Follow the [offcial instructions for starting Docker](https://docs.docker.com/engine/daemon/start/).
+
+#### Podman
+
+Run
+
+```bash
+podman info
+```
 
 ### Build an image from a URL
 
@@ -55,12 +72,12 @@ jupyter-repo2docker https://github.com/binder-examples/requirements
 You'll see `repo2docker` take the following actions:
 
 1. Inspect the repository for [configuration files](#config-files). It will detect the `requirements.txt` file in the repository.
-2. Build a Docker image using the configuration files. In this case, the `requirements.txt` file will correspond to a Python environment.
+2. Build a container image using the configuration files. In this case, the `requirements.txt` file will correspond to a Python environment.
 3. Run the image to let you explore the repository interactively.
 
 Click the link provided and you'll be taken to an interactive Jupyter Notebook interface where you can run commands interactively inside the environment.
 
 ## Learn more
 
 This is a simple example building an environment image for your repository.
-To learn more about the kinds of source repositories, environments, and use-cases that repo2docker supports, see [the `repo2docker` user guide](./use/index.md).
+To learn more about the kinds of source repositories, environments, and use-cases that `repo2docker` supports, see [the `repo2docker` user guide](./use/index.md).