builder: document how to generate the image for podman

Signed-off-by: Yann Dirson <[email protected]>

Author: ydirson

developer/building/qubes-builder-v2.md

@@ -77,21 +77,27 @@ if you don't know which executor to use, use docker.
     ```
     Next, **restart the qube**.
 
-5. Finally, you need to generate a docker image:
+5. Finally, you need to generate a container image, for either `docker` or `podman`.
 
-    ```shell
-   $ tools/generate-container-image.sh docker
-    ```
-
-   In an app qube, as `/var/lib/docker` is not persistent by default, you also
+   If you are using `docker` and an app qube, as `/var/lib/docker` is not persistent by default, you also
    need to use [bind-dirs](/doc/bind-dirs/) to avoid repeating this step after reboot, adding
    the following to the `/rw/config/qubes-bind-dirs.d/docker.conf` file in
-   this qube:
+   this qube, and restarting your Qube before proceeding to the image generation:
 
    ```
    binds+=( '/var/lib/docker' )
    ```
 
+    Note this is not useful with `podman`, which uses `~/.local/share/containers/`.
+
+    Depending on your choice of a container runtime, run one of:
+    ```shell
+   $ tools/generate-container-image.sh docker
+    ```
+    ```shell
+   $ tools/generate-container-image.sh podman
+    ```
+
 # Configuration
 
 To use Qubes OS Builder v2, you need to have a `builder.yml` configuration file.
@@ -127,6 +133,12 @@ executor:
     image: "qubes-builder-fedora:latest"
 ```
 
+If you want use the `podman` executor, you have to enable socket
+activation, with:
+
+```
+systemctl --user enable --now podman.socket
+```
 
 # Using Builder v2