builds volume.

Needed for easier mounting using `--volumes-from` to acces the files
when running another container (launching a container from inside a
container, for an example see the CI from
https://git.shore.co.il/nimrod/resume).

docker-compose.yml

@@ -14,6 +14,7 @@ services:
     image: adarnimrod/gitlab-runner
     restart: always
     volumes:
+      - builds:/builds
       - config:/etc/gitlab-runner
       - /var/run/docker.sock:/var/run/docker.sock
   crond:
@@ -23,6 +24,7 @@ services:
       - /run/docker.sock:/run/docker.sock
 
 volumes:
+  builds:
   config:
 
 networks: