Make Docker Compose more deployable.

Changes to make the Docker Compose setup more deployable in my
infrastructure.

- Share the network with other projects.
- A saner project name.
- Mark the volume for backups.

.env

+COMPOSE_PROJECT_NAME=cgit

docker-compose.yml

@@ -15,3 +15,9 @@ services:
 
 volumes:
   git:
+    labels:
+      snapshot: 'true'
+
+networks:
+  default:
+    name: shore