docs: add .env.example with placeholders

the file documents necessary environment variables for running and testing FHEVM

Author: Everboyzo

.env.example

@@ -0,0 +1,26 @@
+# Example environment configuration for FHEVM
+
+# RPC endpoint for the Ethereum network used by FHEVM contracts.
+FHEVM_ETH_RPC_URL=https://your-ethereum-node-url
+
+# Endpoint for the Zama relayer service.
+FHEVM_RELAYER_URL=https://your-relayer-url
+
+# TFHE worker URL used by the coprocessor (e.g. coprocessor/fhevm-engine).
+TFHE_WORKER_URL=http://localhost:3000
+
+# Private key of the deployer/test account (never commit real keys).
+PRIVATE_KEY=0x...
+
+# Network name: 'local', 'sepolia', 'mainnet', etc.
+NETWORK=local
+
+# Path for persistent storage (used by benchmark parser and golden images).
+DATABASE_URL=./data/db.sqlite
+
+# AWS region and credentials used by CI back‑ends (optional).
+AWS_REGION=eu-west-3
+AWS_ACCESS_KEY_ID=YOUR_AWS_KEY
+AWS_SECRET_ACCESS_KEY=YOUR_AWS_SECRET
+
+# Copy this file to `.env` or `.env.local` and adjust the values as needed.