integrations: Update text for airbrake doc.

With minor fixes by eeshangarg!

Eeshan: I decided to remove the screenshot. It looks very old and
was blurry and the instructions were very screenshot-agnostic
anyway!

I couldn't update the screenshot because Airbrake doesn't even let
you use the free trial till you give them your credit card info,
which I didn't want to do!

zerver/webhooks/airbrake/doc.md

@@ -2,17 +2,15 @@ Get Zulip notifications for your Airbrake bug tracker!
 
 1. {!create-stream.md!}
 
-2. {!create-bot-construct-url-indented.md!}
+1. {!create-bot-construct-url-indented.md!}
 
-3. Now, go to your project's settings on the Airbrake site.
+1. Go to your project's settings on the Airbrake site. Click on the
+   **Integration** section, and select **Webhook**.
 
-4. Click on the **Integration** section.
+1. Enter the URL constructed above, and check **Enabled**.
 
-5. Select **Webhook** and provide the URL constructed above.
-
-6. Check **Enabled**, and save. Your Webhook configuration should look similar to:
-   ![](/static/images/integrations/airbrake/001.png)
+1. Click **Save**.
 
 {!congrats.md!}
 
-![](/static/images/integrations/airbrake/002.png)
+![](/static/images/integrations/airbrake/001.png)