include comment for how to add a beacon node endpoint (#187)

Author: Roberto Bayardo

.env.goerli

@@ -7,6 +7,9 @@ OP_GETH_SEQUENCER_HTTP=https://goerli-sequencer.base.org
 # [recommended] replace with your preferred L1 (Ethereum, not Base) node RPC URL:
 OP_NODE_L1_ETH_RPC=https://ethereum-goerli-rpc.allthatnode.com
 
+# [required] replace with your preferred L1 CL beacon endpoint:
+# OP_NODE_L1_BEACON=https://your.goerli.beacon.node/endpoint-here
+
 # auth secret used by op-geth engine API:
 OP_NODE_L2_ENGINE_AUTH_RAW=688f5d737bad920bdfb2fc2f488d6b6209eebda1dae949a8de91398d932c517a
 

.env.mainnet

@@ -7,6 +7,9 @@ OP_GETH_SEQUENCER_HTTP=https://mainnet-sequencer.base.org
 # [recommended] replace with your preferred L1 (Ethereum, not Base) node RPC URL:
 OP_NODE_L1_ETH_RPC=https://1rpc.io/eth
 
+# [required] replace with your preferred L1 CL beacon endpoint:
+# OP_NODE_L1_BEACON=https://your.mainnet.beacon.node/endpoint-here
+
 # auth secret used by op-geth engine API:
 OP_NODE_L2_ENGINE_AUTH_RAW=688f5d737bad920bdfb2fc2f488d6b6209eebda1dae949a8de91398d932c517a
 

.env.sepolia

@@ -7,6 +7,9 @@ OP_GETH_SEQUENCER_HTTP=https://sepolia-sequencer.base.org
 # [recommended] replace with your preferred L1 (Ethereum, not Base) node RPC URL:
 OP_NODE_L1_ETH_RPC=https://rpc.sepolia.org
 
+# [required] replace with your preferred L1 CL beacon endpoint:
+# OP_NODE_L1_BEACON=https://your.sepolia.beacon.node/endpoint-here
+
 # auth secret used by op-geth engine API:
 OP_NODE_L2_ENGINE_AUTH_RAW=688f5d737bad920bdfb2fc2f488d6b6209eebda1dae949a8de91398d932c517a