Docs update request: /run-arbitrum-node/run-full-node

Source: https://docs.arbitrum.io/run-arbitrum-node/run-full-node

Request: Give clear information about the form of the Beacon Chain RPC Url.

I used Nodereal.io to obtain a Beacon chain rpc endpoint and the structure they give is .../api_key/eth/v1
But that leads to errors while running the Arbitrum validator. We would need to remove the /eth/v1 from the end in order to make it work.