Add command for docker, explain submodules

Signed-off-by: Davide Cavalca <davide@cavalca.name>

Author: davide125

README.md

@@ -10,4 +10,12 @@ This is made with [MkDocs](https://www.mkdocs.org/). If you have mkdocs installe
 $ podman run -it --pull=newer -p=8000:8000 -v=$(pwd)/:/docs:z ghcr.io/asahilinux/mkdocs-asahi:latest
 ```
 
+if you're using [Podman](https://podman.io), or
+
+```
+$ docker run -it --pull=always -p=8000:8000 -v=$(pwd)/:/docs:z ghcr.io/asahilinux/mkdocs-asahi:latest
+```
+
+if you're using [Docker](https://www.docker.com). Note that this repository uses [Git Submodules](https://git-scm.com/book/en/v2/Git-Tools-Submodules), so you'll want to set those up first with `git submodule update --init`.
+
 The website is rebuilt by the CI on every commit and served via GitHub Pages. The container is also automatically updated and pushed to the registry.