help: Use an emoji that does not vary in design.

The octopus emoji varies in design based on the user's device/browser,
while thumbs up emoji is more consistent in that regards.

Author: shubham-padia

help/search-for-messages.md

@@ -41,7 +41,7 @@ Some details to keep in mind:
 - Zulip search ignores very common words like `a`, `the`, and about 100 others.
 - [Emoji](/help/emoji-and-emoticons) in messages (but not [emoji
   reactions](/help/emoji-reactions)) are included in searches, so if you search
-  for `octopus`, your results will include messages with the `:octopus:` emoji (🐙).
+  for `thumbs_up`, your results will include messages with the `:thumbs_up:` emoji (👍).
 
 ## Search filters