Create boilerplate text/link for top of lesson pages

[emilywithrow]

We need to address the issue of someone coming to CSS (or HTML, or any lesson-not-project) as the entry point. Let's add something akin to a warning like "This lesson is part of a larger project on If you feel like you're missing some context, TK TK." etc.

[emilywithrow]

Assigning to @AditiBhandari because I can't find Eunice on here! @JoeGermuska can you add her, please?

[JoeGermuska]

hi @euniceylee

[AditiBhandari]

We're on it!