Add examples for min/max width/height.

docs/examples/styles/max_width.py

@@ -0,0 +1,16 @@
+from textual.app import App
+from textual.containers import Vertical
+from textual.widgets import Placeholder
+
+
+class MaxWidthApp(App):
+    def compose(self):
+        yield Vertical(
+            Placeholder("max-width: 50h", id="p1"),
+            Placeholder("max-width: 999", id="p2"),
+            Placeholder("max-width: 50%", id="p3"),
+            Placeholder("max-width: 30", id="p4"),
+        )
+
+
+app = MaxWidthApp(css_path="max_width.css")