Create readme for hyperscriptify library

Overview

Contributors might need to know more about how this works, and it seems most appropriate to have these docs in the library itself https://github.com/effulgentsia/hyperscriptify
(the library is maintained by a Drupal/XB contributor)

Proposed resolution

Create an PR that adds a readme to the hyperscriptify library, then add it to the copy of the library in XB

User interface changes