Add multi-stage dockerfile build example (getzola#2327)

* Add multi-stage dockerfile build example

* Simplify install instructions, add docker image deployment example

docs/content/documentation/deployment/docker-image.md

@@ -0,0 +1,36 @@
++++
+title = "Docker image"
+weight = 90
++++
+
+If you have to distribute a Zola based web site through Docker, it's easy to do with a multi-stage build.
+
+Here is an example that builds the current folder, and put the result in a docker image that will be served by
+[static-web-server](https://static-web-server.net/), a minimalist web server written in rust.
+
+Of course, you may want to replace the second stage with another static web server like Nginx or Apache.
+
+```Dockerfile
+FROM ghcr.io/getzola/zola:v0.17.1 as zola
+
+COPY . /project
+WORKDIR /project
+RUN ["zola", "build"]
+
+FROM ghcr.io/static-web-server/static-web-server:2
+WORKDIR /
+COPY --from=zola /project/public /public
+```
+
+To build your website as a docker image, you then run:
+```shell
+docker build -t my_website:latest .
+```
+
+To test your site, just run the docker image and browse [http://localhost:8000](http://localhost:8000)
+
+```
+docker run --rm -p 8000:80 my_website:latest
+```
+
+Note that, if you want to be able to use your docker image from multiple locations, you'll have to set `base_url` to `/`.

docs/content/documentation/getting-started/installation.md

@@ -178,6 +178,19 @@ You can now browse http://localhost:8080.
 > port between 1024 and 9000 for live reload. The new docker command would be
 > `$ docker run -u "$(id -u):$(id -g)" -v $PWD:/app --workdir /app -p 8080:8080 -p 1024:1024 ghcr.io/getzola/zola:v0.17.1 serve --interface 0.0.0.0 --port 8080 --base-url localhost`
 
+#### Multi-stage build
+
+Since there is no shell in the Zola docker image, if you want to use it from inside a Dockerfile, you have to use the
+exec form of `RUN`, like:
+
+```Dockerfile
+FROM ghcr.io/getzola/zola:v0.17.1 as zola
+
+COPY . /project
+WORKDIR /project
+RUN ["zola", "build"]
+```
+
 
 ## Windows