Updated search docs with new collection type

docs/search.md

@@ -18,12 +18,18 @@ var request = new SearchIssuesRequest();
 
 // you should focus your search to a specific repo
 request.Repos.Add("aspnet/dnx");
+request.Repos.Add("aspnet", "dnvm");
 
 // or use a series of repositories
-request.Repos = new Collection<string> {
+request.Repos = new RepositoryCollection {
     "aspnet/dnx",
     "aspnet/dnvm"
 };
+
+request.Repos = new RepositoryCollection {
+    { "aspnet", "dnx" },
+    { "aspnet", "dnvm" }
+};
 ```
 
 There's many other options available here to tweak