update outdated information on docker compose

docker compose v2 is no longer its own command but uses a
subcommand of docker

README.md

@@ -38,10 +38,10 @@ To use it, you first have to know what stackmaxima version you need.
 Note that this is different from the moodle stack version, ilias stack version and maxima version.
 The needed stackmaxima version can be seen in the ["What Stackmaxima version do I need?"](#what-stackmaxima-version-do-i-need) section.
 
-They can be simply run with docker-compose in the top-directory of the repository (setting the `STACKMAXIMA_VERSION` to the desired value):
+They can be simply run with docker compose in the top-directory of the repository (setting the `STACKMAXIMA_VERSION` to the desired value):
 ```
 export STACKMAXIMA_VERSION=...
-docker-compose up -d
+docker compose up -d
 ```
 The container should then be available on port 8080 (from outside the host too, keep this behind a firewall so it is not reachable from the general internet).