Fix heading display in TOC (#472)

Co-authored-by: Maayan <maayan@aptoslabs.com>

Author: networkdm

packages/wallet-adapter-react/docs/BYO-wallet-selector.md

@@ -99,7 +99,7 @@ const AptosConnectWalletRow = ({ wallet, onConnect }: WalletItemProps) => {
 
 This is a headless component that serves as a wrapper element and sets up a React context to provide the wallet information to the rest of the `WalletItem.*` components.
 
-### `WalletItem.Icon`
+#### `WalletItem.Icon`
 
 This is a headless component that renders the icon of the wallet.