docs: intro + basic chapter fixes (#10361)

www/packages/docs-ui/src/components/Heading/H2/index.tsx

@@ -17,7 +17,7 @@ export const H2 = ({ className, children, passRef, ...props }: H2Props) => {
   return (
     <h2
       className={clsx(
-        "h2-docs [&_code]:!h2-docs [&_code]:!font-mono mb-docs_1 mt-docs_4 text-medusa-fg-base",
+        "h2-docs [&_code]:!h2-docs [&_code]:!font-mono mb-docs_1 mt-docs_2 text-medusa-fg-base",
         props.id && "group/h2 scroll-m-56",
         className
       )}