Prominently link tooltip docs to Design Guidelines

[shawnbot]

@broccolini mentioned that we should move our new guidance (in #676) for relying less on tooltips to the Design Guidelines. We haven't figured out what it looks like for multiple sites (these CSS and the Tooltip components, in this case) to refer back to more general guidance, but this might be a good place to start working through that.

This might be something that we should consider formalizing in Blueprints, a la a flash alert that points people to relevant guidelines? /cc @emplums

[yaili]

@simurai most of these links are breaking, is this still relevant?

[simurai]

Updated the broken Tooltip components link.

There is some "⚠️ Usage warning! ⚠️", but it sounds like the plan is to also add guidance how to use tooltips to the Design Guidelines. It could be similar to Button usage. So we could transfer this issue to https://github.com/primer/design.

Also, we still haven't really figured out what to do with tooltips that get cut off or on responsive pages. https://github.com/github/design-systems/issues/558

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