cd into project directory and create .env
by running the command below on *NIX systems, or by creating the file manually.
tee .env > /dev/null <<EOT
TESTNET_MNEMONIC="REPLACE WITH MNEMONIC"
ETHERSCAN_API_KEY="REPLACE WITH ETHERSCAN API KEY"
OPTIMISTIC_ETHERSCAN_API_KEY="REPLACE WITH OPTIMISTIC ETHERSCAN API KEY"
EOT
Then edit the keys accordingly in .env