Link the USDT0 docs page to the USDT0 launch guide (#2841)

* Link the USDT0 docs page to the USDT0 launch guide

/launch/usdt0 has no inbound links from anywhere on the site, including
this page, which is its most natural referrer. Readers who land here
looking for partner support or an integration checklist have no way to
find it, and crawlers reach orphaned pages less often.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* use `pathname` to avoid docusaurus build failures

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: Elliot <elliot@stellar.org>

Author: 3 people

docs/tokens/usdt0-layerzero.mdx

@@ -11,6 +11,8 @@ description: "Use USDT0, Tether's USDT delivered over LayerZero's OFT standard,
 
 On Stellar, USDT0 is a **classic asset with a SAC**. Classic flows use a trustline plus a payment. Soroban contracts call the SAC. See the [tokenization model comparison](./anatomy-of-an-asset.mdx#tokenization-model-comparison) for what that implies.
 
+For an overview of what USDT0 unlocks on Stellar, the partners supporting it today, and a deployment checklist, see the [USDT0 on Stellar launch guide](pathname:///launch/usdt0).
+
 :::info[Full documentation]
 
 For the architecture, the OFT interface, supported chains, and the transfer UI: