[docs] Improve typography documentation (#19216)

Kevin Lindsay · oliviertassinari · commit 1c6d5a861d91 · 2020-01-14T11:09:08.000+01:00
diff --git a/docs/src/pages/customization/typography/typography.md b/docs/src/pages/customization/typography/typography.md
@@ -68,6 +68,12 @@ const theme = createMuiTheme({
     },
   },
 });
+
+// ...
+<ThemeProvider theme={theme}>
+  <CssBaseline />
+  {children}
+</ThemeProvider>
 ```
 
 ## Font size
