Indicate how to import fonts (#3676)

Got this fix from issue #2302. Libraries like `font-awesome` are pretty common. Indicating how to get them to work should be indicated in the `README.md` (if not added to the example)

examples/with-global-stylesheet/README.md

@@ -60,3 +60,7 @@ This project shows how you can set it up. Have a look at:
 
 Please, report any issue on enhancement related to this example to its original
 github repository https://github.com/davibe/next.js-css-global-style-test
+
+## If your stylesheets import fonts
+
+Install `postcss-url` and insert `require('postcss-url')({ url: 'inline' })` as the 2nd element of the `plugins` array in `postcss.config.js`.