select.lua: change the --save-watch-history warning text

The current warning was fine when you select history directly, but
giving more information can be useful when you happen to see it by right
clicking the title without prior information.

Fixes #15655 (comment)

player/lua/select.lua

@@ -390,7 +390,7 @@ mp.add_key_binding(nil, "select-watch-history", function ()
     if not history_file then
         show_warning(mp.get_property_native("save-watch-history")
                      and error_message
-                     or "Enable --save-watch-history")
+                     or "Enable --save-watch-history to jump to recently played files.")
         return
     end