Add support for using podman to util/docker_build.sh (#10819)

* add podman support to docker_build.sh script

* break out runtime into the RUNTIME variable
* allows RUNTIME to be set by the user
* decides on docker or podman if docker isn't avaible
* rewrote check for docker-machine to account only for docker runtime
* put --user arg into a variable only to be used with docker
  this is not needed with podman as podman maps the containers root id
  to the users id.

* add podman to getting_started_docker documentation

1 files changed, 9 insertions, 1 deletions

diff --git a/docs/getting_started_docker.md b/docs/getting_started_docker.md
index e5309fdbb..f9c3b366a 100644
--- a/docs/getting_started_docker.md
+++ b/docs/getting_started_docker.md
@@ -4,8 +4,9 @@ This project includes a Docker workflow that will allow you to build a new firmw
 
 ## Requirements
 
-The main prerequisite is a working `docker` install.
+The main prerequisite is a working `docker` or `podman` install.
 * [Docker CE](https://docs.docker.com/install/#supported-platforms)
+* [Podman](https://podman.io/getting-started/installation)
 
 ## Usage
 
@@ -38,6 +39,13 @@ util/docker_build.sh
 # Reads parameters as input (leave blank for all keyboards/keymaps)
 ```
 
+You can manually set which container runtime you want to use by setting the `RUNTIME` environment variable to it's name or path.
+By default docker or podman are automatically detected and docker is preferred over podman.
+
+```bash
+RUNTIME="podman" util/docker_build.sh keyboard:keymap:target
+```
+
 ## FAQ
 
 ### Why can't I flash on Windows/macOS