Move to using Docker Compose v2 explicitly

GitHub have removed v1 from their CI images, see
actions/runner-images#9692.

I thiiink this is what was already expected since the compose file
is labelled as v2, though I don't know enough about docker compose
to be sure.

Author: PeterJCLaw

.github/workflows/publish.yml

@@ -36,10 +36,10 @@ jobs:
     - uses: actions/checkout@v4
 
     - name: Build container
-      run: docker-compose build
+      run: docker compose build
 
     - name: Build site in container
-      run: docker-compose run docs rake build
+      run: docker compose run docs rake build
 
   changes:
     runs-on: ubuntu-latest

README.md

@@ -4,7 +4,7 @@ The Student Robotics public documentation.
 
 ## Getting Started
 
-For ease of setup, a Docker container is provided. Simply install Docker and `docker-compose`, and run `docker-compose up`.
+For ease of setup, a Docker container is provided. Simply install Docker and `docker-compose`, and run `docker compose up`.
 
 Once setup, the site will be accessible on http://localhost:4000/docs/