docs(learn): give the tic-tac-toe nine-squares step its own example

The step says 'number the squares so you can tell them apart' and then shows a
snippet whose component is already renamed to board and whose buttons already
read 1-9 -- i.e. it printed the *result* of the rename step two paragraphs
before the rename was asked for, and the same file was reused for both steps.

Add tutorial_tic_tac_toe/nine_squares/app.py (component still named square,
rows of numbered buttons) and point the first include at it. The later include
keeps pointing at board/app.py.

Also clarify editor-setup: the VSCode extension is published as Pylance, which
bundles Pyright -- the bullet said 'install Pyright using the extension' against
a marketplace item nobody can find by that name.

Author: Archmonger

docs/examples/tutorial_tic_tac_toe/nine_squares/app.py

@@ -0,0 +1,26 @@
+from reactpy import component, html
+
+
+# start
+@component
+def square():
+    return html.fragment(
+        html.div(
+            {"className": "board-row"},
+            html.button({"className": "square"}, "1"),
+            html.button({"className": "square"}, "2"),
+            html.button({"className": "square"}, "3"),
+        ),
+        html.div(
+            {"className": "board-row"},
+            html.button({"className": "square"}, "4"),
+            html.button({"className": "square"}, "5"),
+            html.button({"className": "square"}, "6"),
+        ),
+        html.div(
+            {"className": "board-row"},
+            html.button({"className": "square"}, "7"),
+            html.button({"className": "square"}, "8"),
+            html.button({"className": "square"}, "9"),
+        ),
+    )

docs/src/learn/tutorial-tic-tac-toe.md

@@ -134,7 +134,7 @@ Now copy-paste your way to nine squares and... they come out in a single line, n
 === "app.py"
 
     ```python
-    {% include "../../examples/tutorial_tic_tac_toe/board/app.py" start="# start" %}
+    {% include "../../examples/tutorial_tic_tac_toe/nine_squares/app.py" start="# start" %}
     ```
 
 === "styles.css"