docs: document port and log level variables in env files

Operators who want to customise execution-client ports (e.g. to run
multiple nodes or resolve port conflicts) or change log verbosity had
no way to discover the supported variables without reading
execution-entrypoint directly.

Add commented-out PORT CONFIGURATION and LOG LEVEL sections to both
.env.mainnet and .env.sepolia, listing all variables already supported
by execution-entrypoint with their defaults:

  RPC_PORT, WS_PORT, AUTHRPC_PORT, METRICS_PORT,
  DISCOVERY_PORT, V5_DISCOVERY_PORT, P2P_PORT, LOG_LEVEL

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: erhnysr

.env.mainnet

@@ -48,6 +48,22 @@ STATSD_ADDRESS="172.17.0.1"
 # FLASHBLOCKS (OPTIONAL - UNCOMMENT TO ENABLE)
 # RETH_FB_WEBSOCKET_URL=wss://mainnet.flashblocks.base.org/ws
 
+# PORT CONFIGURATION (OPTIONAL - UNCOMMENT TO OVERRIDE DEFAULTS)
+# ---------------------------------------------------------------
+# Override default ports when running multiple nodes or to resolve conflicts.
+# RPC_PORT=8545          # HTTP JSON-RPC port
+# WS_PORT=8546           # WebSocket JSON-RPC port
+# AUTHRPC_PORT=8551      # Engine API (authenticated RPC) port
+# METRICS_PORT=6060      # Prometheus metrics port
+# DISCOVERY_PORT=30303   # P2P discovery port
+# V5_DISCOVERY_PORT=9200 # discv5 discovery port
+# P2P_PORT=30303         # P2P TCP port
+
+# LOG LEVEL (OPTIONAL - UNCOMMENT TO OVERRIDE DEFAULT)
+# -----------------------------------------------------
+# Supported values: error, warn, info, debug, trace (default: info)
+# LOG_LEVEL=info
+
 # PRUNING (OPTIONAL - UNCOMMENT TO ENABLE)
 # NOTE: Set to any number of blocks you want, but it should be >10064
 # NOTE: The node type that was chosen when first running a node cannot be changed after the initial sync. Turning Archive into Pruned, or Pruned into Full is not supported [source](https://reth.rs/run/faq/pruning/).

.env.sepolia

@@ -48,6 +48,22 @@ STATSD_ADDRESS="172.17.0.1"
 # FLASHBLOCKS (OPTIONAL - UNCOMMENT TO ENABLE)
 # RETH_FB_WEBSOCKET_URL=wss://sepolia.flashblocks.base.org/ws
 
+# PORT CONFIGURATION (OPTIONAL - UNCOMMENT TO OVERRIDE DEFAULTS)
+# ---------------------------------------------------------------
+# Override default ports when running multiple nodes or to resolve conflicts.
+# RPC_PORT=8545          # HTTP JSON-RPC port
+# WS_PORT=8546           # WebSocket JSON-RPC port
+# AUTHRPC_PORT=8551      # Engine API (authenticated RPC) port
+# METRICS_PORT=6060      # Prometheus metrics port
+# DISCOVERY_PORT=30303   # P2P discovery port
+# V5_DISCOVERY_PORT=9200 # discv5 discovery port
+# P2P_PORT=30303         # P2P TCP port
+
+# LOG LEVEL (OPTIONAL - UNCOMMENT TO OVERRIDE DEFAULT)
+# -----------------------------------------------------
+# Supported values: error, warn, info, debug, trace (default: info)
+# LOG_LEVEL=info
+
 # PRUNING (OPTIONAL - UNCOMMENT TO ENABLE)
 # NOTE: Set to any number of blocks you want, but it should be >10064
 # NOTE: The node type that was chosen when first running a node cannot be changed after the initial sync. Turning Archive into Pruned, or Pruned into Full is not supported [source](https://reth.rs/run/faq/pruning/).