Docs update request: /how-arbitrum-works/gas-fees

[PaulRBerg]

Source: https://docs.arbitrum.io/how-arbitrum-works/gas-fees

Request: explain that the L1 fee is baked into the gas limit.

Context: It's not clear from the current documentation how the Arbitrum gas fee model works relative to other rollups like Optimism. You should add a paragraph before all existing content to explain this basic fact, which you currently assume the reader to know.

References:

• feat: gas costs mds1/evm-diff#31 (comment)
• Is there any comprehensive documentation on how gas metering works across EVM chains?
• Why do simple ETH transfers on Arbitrum cost ~37k gas now?