bots: Modify howdoi/readme.md to correctly call 'howdoi' bot.

Update images with new commands screenshots for better understanding.

zulip_bots/zulip_bots/bots/howdoi/readme.md

@@ -10,18 +10,18 @@ Benjamin Gleitzman.
 Simply prepend your questions with one of the following commands. The
 answer will be formatted differently depending the chosen command.
 
-| Command     | Respond                                                |
-| ----------- | ------------------------------------------------------ |
-| `@howdowe`  | Concise answer to the same stream.                     |
-| `@howdowe!` | Same as `@howdowe` but with full answer and URL of the solutions. |
-| `@howdoi`   | Concise answer replied to sender via private message.  |
-| `@howdoi!`  | Same as `@howdoi` but with full answer and URL of the solutions. |
+| Command                 | Respond                                                |
+| ----------------------- | ------------------------------------------------------ |
+| `@mention-bot howdowe`  | Concise answer to the same stream.                     |
+| `@mention-bot howdowe!` | Same as `@mention-bot howdowe` but with full answer and URL of the solutions. |
+| `@mention-bot howdoi`   | Concise answer replied to sender via private message.  |
+| `@mention-bot howdoi!`  | Same as `@mention-bot howdoi` but with full answer and URL of the solutions. |
 
 ## Screenshots
 
 #### Example 1
 
-Question -> `@howdowe use supervisor in elixir`
+Question -> `@mention-bot howdowe use supervisor in elixir`
 
   ![howdowe question](assets/question_howdowe.png)
 
@@ -32,7 +32,7 @@ of the answer.
 
 #### Example 2
 
-Question -> `@howdoi! stack vs heap`
+Question -> `@mention-bot howdoi! stack vs heap`
 
   ![howdoi! question](assets/question_howdoi_all.png)
 
@@ -51,6 +51,6 @@ This could be adjusted in the source code (`HowdoiHandler.MAX_LINE_LENGTH`).
 instead of a complete sentences (eg: "How do i make a decorator in Python"
 -> "python decorator").
 
-* __[*Limitation*]__ If a answer contains multiple code blocks, the `@howdoi`
-and `@howdowe` commands would only return the first coding section, use
-`@howdo[we|i]!` in that case.
+* __[*Limitation*]__ If a answer contains multiple code blocks, the `@mention-bot howdoi`
+and `@mention-bot howdowe` commands would only return the first coding section, use
+`@mention-bot howdo[we|i]!` in that case.