message: Add expose tags to example
diff: @@ -4,7 +4,9 @@ Reshuffle includes a simple key-value store. To use it,
  ```js
  import * as db from '@reshuffle/db';
  +/* @expose */
  function readCounter(key) { return db.get(`counter:${key}`); }
  +/* @expose */
  function incrementCounter(key) { return db.update(`counter:${key}`, (n) => (n || 0) + 1); }
  ```
  Note all `db` calls are asynchronous and promise a result. You should `await` their result.
  