Add link to wiki page from any nonextra module.

modules/buffextras.cpp

@@ -66,5 +66,9 @@ public:
 	}
 };
 
+template<> void TModInfo<CBuffExtras>(CModInfo& Info) {
+	Info.SetWikiPage("buffextras");
+}
+
 MODULEDEFS(CBuffExtras, "Add joins, parts etc. to the playback buffer")