fix(docs): inconsistent table header in connecting-to-base MetaMask section

Path: /base-chain/quickstart/connecting-to-base

**Page:** https://docs.base.org/base-chain/quickstart/connecting-to-base
**File:** `docs/base-chain/quickstart/connecting-to-base.mdx`

## Description

In the MetaMask manual setup table for **Base Sepolia**, the first column header reads `Name` but the first cell value reads `Sepolia` — which is inconsistent with the equivalent table for Base Mainnet, where the first row is a `Description` field.

**Current (Base Sepolia table):**

| Name | Sepolia |
| --- | --- |
| Network Name | Base Sepolia |
| RPC Endpoint | https://sepolia.base.org |
| ... | ... |

**Base Mainnet table for comparison:**

| Name | Value |
| --- | --- |
| Network Name | Base Mainnet |
| Description | The public mainnet for Base. |
| ... | ... |

## Expected behavior

The Base Sepolia table should either:
- Add a missing `Description` row (e.g. `A public testnet for Base.`) to match the Mainnet table, and fix the header to `Name | Value`, or
- Remove the inconsistent `Name | Sepolia` row entirely.

## Suggested fix

Replace the first row of the Base Sepolia MetaMask table:

```
| Name | Value |
```

And add a Description row:

```
| Description | A public testnet for Base. |
```