harden docker-compose.yml (#99)

`user: nobody`: the least privileged account.
`read_only: true`: this container doesn't write anything to the filesystem, this removes a vector.
`security_opt`: disallows the container to grab more privileges.
`cap_drop`: this container doesn't need any capabilities, drop them.
`networks`: put `rimgo` into its own network so it cannot see other containers by default.

Reviewed-on: https://codeberg.org/video-prize-ranch/rimgo/pulls/99
Co-authored-by: kuantum <kuantum@noreply.codeberg.org>
Co-committed-by: kuantum <kuantum@noreply.codeberg.org>

docker-compose.yml

@@ -8,3 +8,14 @@ services:
     ports:
       - 3000:3000
     restart: unless-stopped
+    user: 65534:65534 # equivalent to `nobody`
+    read_only: true
+    security_opt:
+      - no-new-privileges: true
+    cap_drop:
+      - ALL
+    networks:
+      - rimgo
+
+networks:
+  - rimgo