Merge branch 'backend' into db

backend/README.md

@@ -0,0 +1,27 @@
+## Database Schema
+
+```mermaid
+erDiagram
+    user {
+        string name PK
+    }
+
+    game {
+        serial game_id PK
+        int score
+        time playtime
+        date date
+        string username FK
+    }
+
+    user ||--O{ game : "played"
+
+    user_data {
+        string username PK
+        int highscore
+        int total_score
+        int total_playtime
+        int average_score
+        int games_played
+    }
+```