Added leaderboard.

.eslintrc

@@ -0,0 +1,18 @@
+{
+    "root": true,
+    "extends": "airbnb-base",
+    "parser": "@babel/eslint-parser",
+    "parserOptions": {
+        "sourceType": "script"
+    },
+    "env": {
+        "es2020": true
+    },
+    "rules": {
+        "strict": 0,
+        "no-unused-vars": ["error", {"argsIgnorePattern": "^_"}],
+        "no-console": 0,
+        "indent": ["error", 4],
+        "max-len": [2, {"code": 400, "tabWidth": 4, "ignoreUrls": true}]
+    }
+}