Suggest linking to developer-facing materials or research

[jyasskin]

In https://github.com/w3ctag/tag.w3.org/pull/39/files#r1259867959, with a context of

4. Discussion Venues:
   Provide links to external venues such as mailing lists, pull requests, or issue threads where interested readers can catch up on discussions related to the proposed feature.

@LeaVerou suggested:

Maybe also developer-facing materials or research?

In w3ctag/tag.w3.org#57 I suggested that we could mention developer research in the alternatives considered section, and that we could add a Tips section about how to show that the "Practical Use Cases" (in the template as "Solving [goal 1] with this approach") are actually an improvement.

But I'm not sure I correctly understood @LeaVerou's suggestion: This might have been a suggestion that we give developers who find an explainer, breadcrumbs to find better documentation for the feature. If that's it, maybe these links belong at the top of the Proposed Approach section, with a warning that they can't completely replace the explanation in the explainer?