Add banner pointing to new itwêwina

[aarppe]

Since the new itwêwina (itwewina.dev) now surpasses the old itwêwina in all respects (except perhaps providing nêhiyawêwina as an interface language), add a prominent banner that directs a user to the new itwêwina.

The lighter interim solution would be to add such instructions about the new itwêwina in the text box below the search window (in any of the messages.po files).