Fix: adding l2 engine kind param in .env for faster sync (#401)

* fix: adding l2 engine kind param in .env for faster sync

* fix: commenting out with more info about the flag

.env.mainnet

@@ -12,6 +12,10 @@ OP_SEQUENCER_HTTP=https://mainnet-sequencer.base.org
 # [required] replace with your preferred L1 (Ethereum, not Base) node RPC URL:
 OP_NODE_L1_ETH_RPC=https://1rpc.io/eth
 
+# [optional] replace this with your preferred L2 engine kind (geth, reth, etc.)
+# For more info: https://docs.optimism.io/operators/node-operators/configuration/consensus-config#l2enginekind
+# OP_NODE_L2_ENGINE_KIND=reth 
+
 # [required] replace with your preferred L1 CL beacon endpoint:
 OP_NODE_L1_BEACON=https://your.mainnet.beacon.node/endpoint-here