docs: adding intro header

src/pages/references/stacking-contract.md

@@ -6,6 +6,8 @@ description: See a detailed list of all functions and error codes of the Stackin
 export { convertStackingRefToMdx as getStaticProps } from '@common/data/stacking-ref'
 import { StackingErrorcodeReference, StackingFunctionReference } from '@components/stacking-ref'
 
+## Introduction
+
 Stacking is implemented as a smart contract using Clarity. On the testnet, you can always find the Stacking contract by this contract identifier: `ST000000000000000000002AMW42H.pox`.
 
 Below is a list of public and read-only functions as well as error codes that can be returned by those methods.