Update lists/practice.json

lists/practice.json

@@ -21,6 +21,11 @@
       "description": "Competitive programming platform with contests and problem sets",
       "link": "https://codeforces.com/"
     },
+    {
+      "name": "Project Euler",
+      "description": "Math inclined problem sets",
+      "link": "https://projecteuler.net/"
+    },
     {
       "name": "TypeRacer",
       "description": "Speed typing platform",