Search box should have easy access to search hints.

[alexanderkjeldaas]

From commercialhaskell/stackage-content#40

It's difficult to know how to narrow a search on stackage.org.

There should be some explanatory text that covers at least how to narrow search down to a specific package.

Ideally it should be possible to "star" a package to prefer results from that package.

[snoyberg]

PR certainly welcome if you'd like to add some explanatory text along these lines. Package-specific search can be performed already on the per-package pages.