docs: Improve docker compose deployment documentation (#4561)

docs/src/content/docs/self-hosting/docker.md

@@ -20,12 +20,14 @@ Copy the `.env.example` file to `.env` and adjust the variables to your needs.
 cp .env.example .env
 ```
 
+For a new deployment the mandatory variables to fill out are `POSTGRES_PASSWORD` and `SCRUMLR_PRIVATE_KEY`.
+
 ## Generating needed secrets
 
 ### Postgres Password
 
-Generate a secure password for the Postgres database.
-Make sure to set the `POSTGRES_PASSWORD`variable in your .env file to the generated password.
+Make sure to set the `POSTGRES_PASSWORD`variable in your `.env` file to a secure password. For example you can generate a 64 characters long one from the terminal with the following command (if you have `pwgen` installed):
+
 ```sh
 pwgen -s 64 1
 ```
@@ -35,25 +37,41 @@ We use an ECDSA private key to sign the JWT tokens.
 ```sh
 openssl ecparam -genkey -name secp521r1 -noout -out jwt.key
 ```
-Now we need to encode this key to be able to use it as a string in the .env file.
+Now we need to encode this key to be able to use it as a string in the `.env` file:
 ```sh
 cat jwt.key | awk '{printf "%s\\n", $0}'
 ```
 
+Copy the result of this command and paste it into your `.env` file (with `\n` line breaks included) like this, surrounded with quotes:
+
+```ini
+SCRUMLR_PRIVATE_KEY="-----BEGIN EC PRIVATE KEY-----\n...\n-----END EC PRIVATE KEY-----\n"
+```
+
 ## Deployment
 You can now start the deployment using the following command.
 ```sh
 docker-compose up -d
 ```
 
+After a few seconds you can check with `docker ps --all` to see if all the containers have started up. If one crashed or if there is an issue you can check logs with `docker logs (container name or id)`
+
 ## Reverse Proxy
 We strongly recommend using a reverse proxy to handle TLS termination and to provide a secure connection to your users.
-Scrumlr should work with all major reverse proxies like Nginx, Traefik, or Caddy.
+Scrumlr should work with all major reverse proxies like [Nginx](https://nginx.org), [Traefik](https://traefik.io/traefik/) or [Caddy](https://caddyserver.com/docs/quick-starts/reverse-proxy).
 We automatically include a caddy deployment in the docker-compose file, which you can use as a reverse proxy.
-All you need to do is updating the Caddyfile to include your host domain instead of `0.0.0.0:80`.
-If you dont want TLS you can simply keep the specified port.
+All you need to do is updating the `Caddyfile` to include your host domain instead of `0.0.0.0:80`.
+If you don't want TLS you can simply keep the specified port.
 Keep in mind that running Scrumlr without TLS is **not recommended**.
+
 ```
 your_domain {
 }
 ```
+
+## Troubleshooting
+
+### Scrumlr works fine on my machine, but others get an error when they click on "Start now"
+
+Make sure the `SCRUMLR_SERVER_URL` in the `.env` file uses your external ip address, instead of `localhost` or `127.0.0.1`.
+You can search "what is my ip" on the internet to find your external ip address.