fix heading level for stellar multicall / router sdk section (#2685)

Author: leighmcculloch

docs/tools/sdks/contract-sdks.mdx

@@ -79,7 +79,7 @@ Refer to the [OpenZeppelin for Stellar Contracts](../openzeppelin-contracts.mdx#
 
 Axelar has created a Rust crate with useful macros for Stellar smart contract development. Please see Rust Crate [`stellar_axelar_std_derive`](https://axelarnetwork.github.io/axelar-amplifier-stellar/stellar_axelar_std_derive/index.html) for Attribute Macros and Derive Macros, and additional information.
 
-### Stellar Multicall / Router SDK
+## Stellar Multicall / Router SDK
 
 The Stellar Router SDK is a lightweight multicall contract that enables developers to execute multiple Soroban contract calls within a single transaction. While Soroban normally allows only one contract invocation per transaction, the Router bundles multiple calls through a single entry point, effectively enable complex, multi-step workflows to be executed atomically.