Link between stable and unstable documentation

[caspervonb]

Right now the best way to navigate the runtime documentation on deno.land I've come up with is just have the urls memorized. Would be nice to have a link from builtin/stable to builtin/unstable and vice versa at the top near the logo.

Something like

<h3>Stable</h3>
<small><a href="/builtin/unstable">View unstable documentation</a></small>

[tokiedokie]

@caspervonb I think that would be nice. however your issue should go to https://github.com/denoland/doc_website https://doc.deno.land/ is not maintained in this repository.