Fix docker compose file in readme

README.md

@@ -183,7 +183,7 @@ services:
   spothole:
     container_name: spothole
     build:
-      context: https://git.ianrenton.com/ian/spothole.git#latest
+      context: https://git.ianrenton.com/ian/spothole.git#main
     restart: unless-stopped
     ports:
       - "8080:8080"
@@ -192,6 +192,9 @@ services:
       - ./cache:/app/cache
 ```
 
+You can replace `#main` with any other branch or tag reference, for example `#1.5` to pin the build to tagged version
+1.5.
+
 Save the file. You will still need to create a copy of `config-example.yml` and name it `config.yml`, though with the
 Docker setup nothing has actually been downloaded yet, so you will have to copy the example from the repository some
 other way, e.g. [from the repo in a web browser](https://git.ianrenton.com/ian/spothole/src/branch/main/config-example.yml).