docs: add docker guide

Author: lowlighter

.github/readme/partials/documentation/setup.md

@@ -12,7 +12,7 @@ There are several ways to setup metrics, each having its advantages and disadvan
 * [🏗️ Deploying a web instance *(~20 min)*](/.github/readme/partials/documentation/setup/web.md)
   * ✔️ Create another shared instance
   * ➖ Requires some sysadmin knowlegde
-* [🐳 Using command line with docker *(~5 min)*](/.github/readme/partials/documentation/setup/docker.md)
+* [🐳 Using command line with docker *(~2 min)*](/.github/readme/partials/documentation/setup/docker.md)
   * ✔️ Suited for one-time rendering
 * [🔧 Local setup for development *(~20 min)*](/.github/readme/partials/documentation/setup/local.md)
 

.github/readme/partials/documentation/setup/docker.md

@@ -1,3 +1,14 @@
-# 🐳 Using command line with docker (~5 min)
+# 🐳 Using command line with docker (~2 min)
 
-*Documentation not available yet*
+## 0️ Prepare your machine
+
+A server with a recent version of [docker](https://www.docker.com/) is required.
+
+## 1️ Run docker image
+
+The command to use is similar to the following:
+```shell
+docker run --env INPUT_TOKEN=**** --env INPUT_USER=user --volume=/tmp:/metrics_renders ghcr.io/lowlighter/metrics:latest
+```
+
+To pass parameters, pass environment variable with the same name as the corresponding action option but in uppercase and prefixed with `INPUT_`.