ENH: add useful config for running mariadb in docker

.docker/docker-compose.yml

+version: '3.6'
+services:
+  sqldb:
+    image: mariadb:10.5
+    volumes:
+      - type: volume
+        source: "caosdb-sqldata"
+        target: /var/lib/mysql
+    environment:
+      MYSQL_ROOT_PASSWORD: caosdb1234
+    networks:
+      # available on port 3306, host name 'sqldb'
+      - caosnet
+    ports:
+      - 3306:3306
+
+
+# A well-defined network for caosdb
+volumes:
+    caosdb-sqldata:
+networks:
+  caosnet:
+    driver: bridge

README_SETUP.md

@@ -87,6 +87,18 @@ with the then current version of the stored entities.
     * Alternatively, to run the tests in a containerized MariaDB instance, run `make test-docker`,
       followed by `make test-docker-stop`.
 
+
+### Running in a Docker Container
+You can use `.docker/docker-compose.yml` to start a docker container
+(`docker-compose -f .docker/docker-compose.yml up -d`) that runs
+mariadb and you can connect to it with 
+`mariadb -h localhost -P3306 -u caosdb -prandom1234 caosdb`. You need appropriate
+settings in `.config`.
+Due to [a Bug](https://gitlab.com/linkahead/linkahead-mariadbbackend/-/issues/33)
+`MYSQL_CMD="mariadb -h localhost -P3306"` and
+`DATABASE_USER_HOST_LIST=%,`
+
+
 ### Troubleshooting
 
 #### MySQL has failing tests