chore: add api key variable in example.env

Author: CoderUni

web/example.env

@@ -1,4 +1,7 @@
 NEXT_PUBLIC_VLLM_URL="https://<random-id>.ngrok-free.dev" # Remove the trailing slash
 NEXT_PUBLIC_VLLM_MODEL="BigJuicyData/Anni"
 NEXT_PUBLIC_VLLM_TOKEN_LIMIT="32000"
-NEXT_PUBLIC_SYSTEM_PROMPT="You are an expert Python programmer. You will be given a question (problem specification) and will generate a correct Python program that matches the specification and passes all tests."
+NEXT_PUBLIC_SYSTEM_PROMPT="You are an expert Python programmer. You will be given a question (problem specification) and will generate a correct Python program that matches the specification and passes all tests."
+
+# Uncomment this if your vLLM server requires an API key
+#VLLM_API_KEY="REPLACE_WITH_API_KEY"