Add ES modules instructions in browser docs (#6268)

* Add ES6 instructions in browser docs

* Change ES6 to ES6 Modules in browser docs

Co-Authored-By: Jed Fox <git@twopointzero.us>

* Run prettier --write docs/browser.md

docs/browser.md

@@ -24,6 +24,18 @@ prettier.format("query { }", { parser: "graphql", plugins: prettierPlugins });
 </script>
 ```
 
+### ES Modules
+
+```js
+import prettier from "prettier/standalone";
+import parserGraphql from "prettier/parser-graphql";
+
+prettier.format("query { }", {
+  parser: "graphql",
+  plugins: [parserGraphql]
+});
+```
+
 ### AMD
 
 ```js