emulsify-twig-extensions needs a proper READMEd

[callinmullaney]

The emulsify-twig-extensions is a lerna or "mono repo" that houses both our BEM and Add Attribute twig.js functions that are published to npm. It is a sibling repo to emulsify-twig which is the PHP version for Drupal.

A README file should be added to this project that explains the above in more detail and the release workflow.

[callinmullaney]

NPM packages published from this repo:
https://www.npmjs.com/package/bem-twig-extension
https://www.npmjs.com/package/add-attributes-twig-extension