Clearly document how to customise the theme in the README
>>> [!note] Migrated issue
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Reported by: [pameeela](https://www.drupal.org/user/1431110)
Related to !97
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p>The README is currently mostly about Storybook. It does not contain basic information about how to customise the theme (e.g. how to build the CSS).</p>
<p>We should update it to include very clear steps for how to fork/customise the theme and probably move the Storybook information to a separate file.</p>
issue