update Docker documentation

docs/running-gathio/installation.md

@@ -90,39 +90,41 @@ the subject](https://www.linode.com/docs/web-servers/nginx/use-nginx-reverse-pro
 
 ## Docker
 
-The easiest way to run Gathio using Docker is by using the provided `docker-compose` configuration.
+The easiest way to run Gathio using Docker is by using the provided
+`docker-compose` configuration.
 
-Ensure that the `node_modules` folder does not exist in the `gathio` directory before
-starting up the Docker container.
+Create a directory on your system where you'll keep the Gathio configuration
+file and another where Gathio can store user-uploaded event images. Copy the
+example config file into the config directory:
 
-Create a directory on your system where you'll keep the Gathio configuration file. Copy the example
-config file into this directory:
-
-```
-mkdir ~/docker/gathio-docker
-cp config/config.example.toml ~/docker/gathio-docker/config.toml
+```bash
+mkdir -p ~/docker/gathio-docker/{config,images}
+cp config/config.example.toml ~/docker/gathio-docker/config/config.toml
 ```
 
 Under the `volumes` section of the `docker-compose.yml` configuration, adjust the
 configuration volume to match the folder you created:
 
 ```dockerfile
 volumes:
-    - '/home/username/docker/gathio-docker:/app/config
+    - '/home/username/docker/gathio-docker/config:/app/config'
+    - '/home/username/docker/gathio-docker/images:/app/public/events'
 ```
 
-Adjust any settings in the config file, especially the MongoDB URL, which should read as follows for the standard Dockerfile config, and the email service if you want
-to enable it:
+Adjust any settings in the config file, especially the MongoDB URL, which should
+read as follows for the standard Dockerfile config, and the email service if you
+want to enable it:
 
-```
+```ini
 mail_service = "nodemailer"
 mongodb_url = "mongodb://mongo:27017/gathio"
 ```
 
 Finally, start the Docker stack:
 
-```
+```bash
 docker-compose up -d --build
 ```
 
-Gathio should now be running on `http://localhost:3000`, and storing data in a Docker volume.
+Gathio should now be running on `http://localhost:3000`, and storing data in a
+Docker volume.