Clarify wording when a user initiates a thumbnail rescrape.

Previously it could seem like the browser will get notified when complete.

r2/r2/templates/printablebuttons.html

@@ -74,7 +74,7 @@
     </li>
   %endif
   %if thing.show_rescrape:
-    <li>${ynbutton(_("retry thumb"), _("retrying"), "rescrape")}</li>
+    <li>${ynbutton(_("retry thumb"), _("check back in a few minutes"), "rescrape")}</li>
   %endif
 </%def>