docs: Conform *Restrict user email addresses to certain domains* doc to documentation styling guidelines.

templates/zerver/help/restrict-user-email-addresses-to-certain-domains.md

@@ -10,25 +10,18 @@ We allow administrators to block new users from signing up who are not in
 2. Restricting user email addresses to certain domains can be enabled or disabled
  with the **Users restricted to (allowed domains)** checkbox shown below:
 
-    ![Restrict domains checkbox](/static/images/help/restrict-domains-checkbox.png)
-
     !!! tip ""
         The allowed domains will be listed after the **Users restricted to**
          next to the checkbox.
 
-3. Domains can be added to the allowed domains list by clicking on the
+3. Domains can be added to the allowed domains list by clicking on the **Change
- **Change domains** link next to the checkbox. The **Allowed Domains**
+domains** link next to the checkbox to reveal the **Allowed Domains** list.
- list will now appear. You can then add a domain to the list by typing the
- domain into the box underneath the list and clicking the **Add** button.
-
-    ![Allowed domains list](/static/images/help/allowed-domains-list.png)
-
-4. Domains can be deleted from the **Allowed Domains** list by clicking
- the **Delete** button next to a domain on the list.
-
-
-    !!! warn ""
-        Note: You must have at least one allowed domain if
-         **Users restricted to** is enabled
 
+4. You can then add a domain to the list by typing the domain into the box
+underneath the list and clicking the **Add** button.
 
+    !!! tip ""
+        Domains can be deleted from the **Allowed Domains** list by clicking the
+        **Delete** button next to a domain on the list. However, you must have
+        at least one allowed domain if the **Users restricted to** option is
+        enabled.