tutorial: Clarify the initial reply instructions.

The first change might somewhat address users asking "does it matter
which one I click on?" by not being specific that one should click on
_this message_.

The latter I think addresses a small confusion I've seen where people
try try to hit tab before starting a reply.

(imported from commit 708acdf4d4c80713795b96b1a59d681a88604670)

zephyr/static/js/tutorial.js

@@ -112,12 +112,12 @@ function make_script() {
   go(send_message, 'At any time, you can stop this tutorial by replying to me with the word "exit".'),
   go(sleep, 3000),
   go(send_message, "Why don't you **reply to me and say hello?** "
-    + "(Click on this message to reply.)"),
+    + "(Click on a message to reply.)"),
   go2(wait_for_message, 120, pm_to_me),
   go(sleep, 1000),
   go(send_message, 'Great, thanks! After you\'ve typed your reply, you can send it by clicking "Send", but you can also send from the keyboard by pressing `Tab` and then `Enter`.'),
   go(sleep, 4000),
-  go(send_message, "Give it a shot!\n**Send me a reply, and use Tab, then Enter to send it.**"),
+  go(send_message, "Give it a shot!\n**Reply to me again, and use Tab, then Enter to send it.**"),
   go2(wait_for_message, 120, pm_to_me),
   go(sleep, 1000),
   go(send_message, "Nice work. In Humbug, time flows down. Your new messages will always appear at the very bottom of the screen, and we don't automatically scroll. We're always receiving messages for you -- even when you're logged out."),