fix(docs): typo "Etherum" should be "Ethereum" in diffs-ethereum-base

Path: /base-chain/network-information/diffs-ethereum-base

**Page:** https://docs.base.org/base-chain/network-information/diffs-ethereum-base
**File:** `docs/base-chain/network-information/diffs-ethereum-base.mdx`

## Description

There is a typo in the opening sentence of the page.

**Current:**
> Base is built to be as compatible as possible to **Etherum**

**Should be:**
> Base is built to be as compatible as possible to **Ethereum**

## Suggested fix

Replace `Etherum` with `Ethereum` in the first line of the page body.