feat: how-to use Usdt

[Shvandre]

Closes #191

[github-actions]

To fix the formatting issues:

1. Install necessary dependencies: npm ci
2. Then, run this command:

npx remark -o --silent --silently-ignore ecosystem/processing/overview.mdx ecosystem/explorers/tonviewer.mdx guides/usdt.mdx 

[github-actions]

Thanks for the improvements to guides/usdt.mdx. I spotted several high‑severity style‑guide issues that should be addressed before merge.

Findings (4)

High (4)

[HIGH] Unsupported Aside type and missing required safety-callout fields

Location:

docs/guides/usdt.mdx

Lines 13 to 24 in 6e8c1f5

	<Aside
	type="warning"
	title="Verify the Jetton Master address!"
	>
	The authentic USDT Jetton Master address is:
	```
	EQCxE6mUtQJKFnGfaROTKOt1lZbDiiX1kCixRv7Nw2Id_sDs
	```
	**Any token with a different Jetton Master address is NOT real USDT.** Always verify this address before accepting or purchasing USDT. Scammers can create fake tokens with similar names.
	</Aside>

Description:
The top callout uses type="warning", which is not supported. Because this warns about potential loss of funds, it should use a supported type and include the required safety-callout elements: risk, scope, rollback/mitigation, and an environment label.

Suggestion:

 <Aside
-  type="warning"
-  title="Verify the Jetton Master address!"
+  type="danger"
+  title="Verify the Jetton Master address!"
 >
   The authentic USDT Jetton Master address is:
 

EQCxE6mUtQJKFnGfaROTKOt1lZbDiiX1kCixRv7Nw2Id_sDs

**Any token with a different Jetton Master address is NOT real USDT.** Always verify this address before accepting or purchasing USDT. Scammers can create fake tokens with similar names.
+
+  Risk: Accepting tokens from a fake Jetton Master can cause loss of funds.
+  Scope: Applies to USDT transfers and balances on mainnet.
+  Rollback: None on mainnet; on-chain transfers are irreversible. Verify before accepting.
+  Do first (testnet): Use a test jetton on testnet to validate flows safely.
</Aside>

[HIGH] Missing safety callout for funds-moving steps

Location:

docs/guides/usdt.mdx

Lines 74 to 76 in 6e8c1f5

	## How to send USDT
	Sending USDT requires you to interact with your personal USDT jetton wallet. Here's how:

Description:
The “How to send USDT” section directs users to transfer funds without the required safety callout. Per the style guide, any funds-moving step must include risk, scope, rollback/mitigation, and an environment label.

Suggestion:

 ## How to send USDT
+
+<Aside type="danger" title="Funds at risk">
+  Risk: Sending USDT transfers funds irreversibly on mainnet.
+  Scope: Affects your wallet balance and the recipient address.
+  Rollback: None. Send a small test amount first to validate the address and fees.
+  Environment: USDT is not available on testnet. Verify the recipient and the USDT Jetton Master address before mainnet transfers.
+</Aside>

[HIGH] Placeholder not defined on first use

Location:

docs/guides/usdt.mdx

Lines 62 to 64 in 6e8c1f5

	const USDT_MASTER = Address.parse('EQCxE6mUtQJKFnGfaROTKOt1lZbDiiX1kCixRv7Nw2Id_sDs');
	const myWalletAddress = Address.parse('YOUR_TON_WALLET_ADDRESS');

Description:
The code introduces the placeholder YOUR_TON_WALLET_ADDRESS without defining it at first use. The style guide requires defining placeholders on first use to prevent copy/paste mistakes.

Suggestion:

 console.log('My USDT wallet:', myUsdtWalletAddress.toString());

+Define placeholders (first use):
+YOUR_TON_WALLET_ADDRESS — your TON wallet address (basechain) in friendly format.

#### [HIGH] Example not copy-pasteable: missing import for beginCell

Location: https://github.com/ton-org/docs/blob/6e8c1f51d23230d1b20896b962eb9825e1f3aecc/guides/usdt.mdx?plain=1#L54-L72

Description:
The TypeScript snippet calls `beginCell()` without importing it, causing a compile/runtime error. Examples must be self-contained and copy-pasteable.

Suggestion:
```diff
- import { Address } from "@ton/core";
+ import { Address, beginCell } from "@ton/core";