Made compose file adhere to official specs

compose.yaml

@@ -0,0 +1,29 @@
+services:
+    simply-shorten:
+        image: sintan1729/simply-shorten:latest
+        restart: unless-stopped
+        container_name: simply-shorten
+        ports:
+            - 4567:4567
+        environment:
+            # Change if you want to mount the database somewhere else
+            # In this case, you can get rid of the db volume below
+            # - db_url=/urls.sqlite
+            # Change it in case you want to set the website name
+            # displayed in front of the shorturls, defaults to
+            # the hostname you're accessing it from
+            # - site_url=https://www.example.com
+            - username=admin
+            - password=$3CuReP4S$W0rD
+        volumes:
+            - db:/urls.sqlite
+        networks:
+            - proxy
+
+volumes:
+    db:
+
+
+networks:
+    proxy:
+        external: true