[Portal] Update useSendTransaction docs (#4380)

## Problem solved

Short description of the bug fixed or feature added

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## PR-Codex overview
The focus of this PR is to update the example and improve clarity in the `useSendTransaction` hook documentation.

### Detailed summary
- Updated the example from "Using a prepared contract call" to "Sending a prepared contract call"
- Added comments for clarity in the example code
- Added `chain` and `client` properties to the prepared transaction object

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Author: kien-ngo

packages/thirdweb/src/react/web/hooks/transaction/useSendTransaction.tsx

@@ -19,7 +19,7 @@ import { TransactionModal } from "../../ui/TransactionButton/TransactionModal.js
  * Refer to [`SendTransactionConfig`](https://portal.thirdweb.com/references/typescript/v5/SendTransactionConfig) for more details.
  * @example
  *
- * ### Using a prepared contract call
+ * ### Sending a prepared contract call
  *
  * ```tsx
  * import { useSendTransaction } from "thirdweb/react";
@@ -83,11 +83,12 @@ import { TransactionModal } from "../../ui/TransactionButton/TransactionModal.js
  * const { mutate: sendTx, data: transactionResult } = useSendTransaction();
  *
  * const onClick = () => {
+ *   // Send 0.1 SepoliaETH to an address
  *   const transaction = prepareTransaction({
- *       contract,
- *       to: "0x...",
- *       value: toWei("0.1"),
- *     }),
+ *     to: "0x...",
+ *     value: toWei("0.1"),
+ *     chain: sepolia,
+ *     client: thirdwebClient,
  *   });
  *   sendTx(transaction);
  * };