Rustdoc Search: Add Hint to Primitive Type Result

Closes rust-lang#25167

Author: killercup

src/librustdoc/html/static/main.css

@@ -443,6 +443,8 @@ a {
 .content .search-results td:first-child { padding-right: 0; }
 .content .search-results td:first-child a { padding-right: 10px; }
 
+tr.result span.primitive::after { content: ' (primitive type)'; font-style: italic; }
+
 #help {
     background: #e9e9e9;
     border-radius: 4px;