add adminer

Docker/adminer/docker-compose.yml

@@ -0,0 +1,18 @@
+# Use root/example as user/password credentials
+
+version: '3.1'
+
+services:
+  adminer:
+    image: adminer
+    restart: unless-stopped
+    ports:
+      - 8080:8080
+    networks:
+      nginx:
+        aliases:
+          - adminer
+
+networks:
+  nginx:
+    external: true