Update tutorial instructions to use icon for adding children pages

- Reflects changes added in #11012

docs/getting_started/tutorial.md

@@ -342,7 +342,7 @@ Now that this is complete, here is how you can create a page from the Wagtail [a
 
 1.  Go to <http://127.0.0.1:8000/admin> and sign in with your admin user details.
 2.  In the Wagtail [admin interface](https://guide.wagtail.org/en-latest/concepts/wagtail-interfaces/#admin-interface), go to Pages, then click Home.
-3.  Add a child page to the Home page by clicking **...** at the top of the screen and selecting the option **Add child page**.
+3.  Add a child page to the Home page by clicking the **`+`** icon (Add child page) at the top of the screen.
 4.  Choose **Blog index page** from the list of the page types.
 5.  Use "Blog" as your page title, make sure it has the slug "blog" on the Promote tab, and publish it.
 

docs/tutorial/create_contact_page.md

@@ -121,9 +121,8 @@ To add contact information to your portfolio site, follow these steps:
     b. Go to your admin interface.  
     c. Click `Pages` in your [Sidebar](https://guide.wagtail.org/en-latest/how-to-guides/find-your-way-around/#the-sidebar).  
     d. Click `Home`.  
-    e. Click the `...` icon at the top of the resulting page.  
-    f. Click `add child page`.  
-    g. Click `Form page`.
+    e. Click the `+` icon (Add child page) at the top of the resulting page.
+    f. Click `Form page`.
 
 2. Add the necessary data.
 3. Publish your `Form Page`.

docs/tutorial/create_portfolio_page.md

@@ -335,9 +335,8 @@ To add your resume to your portfolio site, follow these steps:
     b. Go to your admin interface.  
     c. Click `Pages` in your [Sidebar](https://guide.wagtail.org/en-latest/how-to-guides/find-your-way-around/#the-sidebar).  
     d. Click `Home`.  
-    e. Click the `...` icon at the top of the resulting page.  
-    f. Click `add child page`.  
-    g. Click `Portfolio Page`.
+    e. Click the `+` icon (Add child page) at the top of the resulting page.
+    f. Click `Portfolio Page`.
 
 2. Add your resume data by following these steps:  
    a. Use "Resume" as your page title.