Moved warning down to be more visible

Why is this change being made?

When users search for GitLab Markdown, this page comes up first, when we'd prefer that the GitLab Flavored Markdown page be returned instead. This MR changes the wording of the warning slightly and moves it below the heading so it might call better attention to it.

Related to: #13031 (closed)

Before	After

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

---

sites/handbook/source/handbook/markdown-guide/index.html.md

@@ -10,11 +10,11 @@ description: "Read through our Markdown kramdown Style Guide!"
 - TOC
 {:toc .hidden-md .hidden-lg}
-If you are using GitLab self-managed or SaaS, please follow the [GitLab Markdown documentation](https://docs.gitlab.com/ee/user/markdown.html). The GitLab handbook uses a different Markdown engine described below. 
-{: .alert .alert-warning}
-
 ## Markdown Style Guide for [about.GitLab.com]
+This style guide is for `about.gitlab.com`. For styles in the GitLab UI, see the [GitLab Flavored Markdown documentation](https://docs.gitlab.com/ee/user/markdown.html). 
+{: .alert .alert-warning}
+
 This website was generated by [Middleman], a blog-aware Static Site Generator ([SSG]) widely used by web developers.
 [Markup language] is part of the structure of any SSG. It is a system to write documents making them somehow
 syntactically distinguishable from text. [Lightweight markup languages] have a simplified and unobtrusive syntax,