build: Add tmpfs to compose file (#1165)

docker-compose.yml

@@ -7,6 +7,10 @@ services:
       - user-avatars:/app/public/user-avatars
       - background-images:/app/public/background-images
       - attachments:/app/private/attachments
+    # Optionally override this to your user/group
+    # user: 1000:1000
+    # tmpfs:
+    #   - /app/.tmp:mode=770,uid=1000,gid=1000
     ports:
       - 3000:1337
     environment: