webhooks/basecamp: Reformat documentation steps into numbered list.

This is a part of our efforts to migrate our webhook docs to have
a more structured numbered-list format similar to our /help
docs.

zerver/webhooks/basecamp/doc.md

@@ -1,24 +1,28 @@
 Zulip supports integration with Basecamp and can notify you of
 events in Basecamp.
 
-{!create-stream.md!}
+1. {!create-stream.md!}
 
-{!create-bot-construct-url.md!}
+2. {!create-bot-construct-url-indented.md!}
 
-Next, go to your project on Basecamp and choose **Set up webhooks**
-from the **Settings** menu that is located in top right corner.
+3. Next, go to your project on Basecamp and choose **Set up webhooks**
+   from the **Settings** menu that is located in top right corner:
 
-![](/static/images/integrations/basecamp/001.png)
+    ![](/static/images/integrations/basecamp/001.png)
 
-Click on **Add a new webhook** button
+4. Click on the **Add a new webhook** button:
 
-![](/static/images/integrations/basecamp/002.png)
+    ![](/static/images/integrations/basecamp/002.png)
 
-Paste the URL you created earlier and choose which events you want
-to be notified about. Make sure that **Enable this webhook?** is
-checked. Click **Add this webhook**.
+5. Paste the URL you created above and select the events you would
+   like to be notified about:
 
-![](/static/images/integrations/basecamp/003.png)
+    ![](/static/images/integrations/basecamp/003.png)
+
+6. Make sure that the checkbox under **Enable this webhook?** is
+   checked.
+
+7. Click **Add this webhook**.
 
 {!congrats.md!}