Explain why search results with an exact package name match are at the top

[daveverwer]

I think it still makes sense that exact matches are at the top, although it may be worth re-visiting that decision, too!

However, with the current implementation it's not clear why the top two packages in this search are at the top of the results. The first one is very new, and wouldn't be top without this rule, and the second one doesn't build on any version of Swift that we support.

We should indicate with maybe a lozenge next to the search results that these are "Exact Package name match" so people know why they're at the top.

[heckj]

Amusingly, I was going back and checking on my SPISearch search for helping with evaluating ranking, and the search results have changed sufficiently that it's not parsing results at the moment. There's been enough interesting new stuff that I'm thinking about tackling another pass at ranking/relevancy again ;-)