Add docs for Pretty, fix some reference issues in docs (#2678)

docs/examples/widgets/pretty.py

@@ -0,0 +1,24 @@
+from textual.app import App, ComposeResult
+from textual.widgets import Pretty
+
+DATA = {
+    "title": "Back to the Future",
+    "releaseYear": 1985,
+    "director": "Robert Zemeckis",
+    "genre": "Adventure, Comedy, Sci-Fi",
+    "cast": [
+        {"actor": "Michael J. Fox", "character": "Marty McFly"},
+        {"actor": "Christopher Lloyd", "character": "Dr. Emmett Brown"},
+    ],
+}
+
+
+class PrettyExample(App):
+    def compose(self) -> ComposeResult:
+        yield Pretty(DATA)
+
+
+app = PrettyExample()
+
+if __name__ == "__main__":
+    app.run()