Update docs/hooks.txt for ShowSearchHitTitle

Update docs/hooks.txt for ShowSearchHitTitle

Reasons:
* $text is vague. It's the label of the link. There is a function named
  getTitleSnippet, which is what I'm reusing for the variable name.
* $page is vague. It's not the page of the search result, but the search
  special page.
* $queryString is not a string but an array of strings.

I also updated https://www.mediawiki.org/wiki/Manual:Hooks/ShowSearchHitTitle
accordingly.

Change-Id: Ia18dbf5ccf7f9fcc8890ad01641d0b7ff3e6eee8